Before Legal Parking, Masuyama enjoyed installing his work in a public place as a guerrilla-stlyle tactic. Masuyama was interested in the reaction of random strangers to his work - a work that was actually an elaborately planned trap in a public space. For a long time, Masuyama had no interest in showing his work in galleries and museums. He thought that it meant nothing if the works in a gallery and a museum drew a response from gallery goers as this was a predictable outcome of the institutional situation.

In this sense, he thought that it would be meaningful to make people outside of the art world involved in his work. One of his tactics was to have an exhibition that used both the outside and the inside of a gallery. Since Masuyama was always compelled by public spaces, it was natural for him to have the inspiration to use parking lots on the street for his projects. He asked the police if he could place his work there. Their response was that nothing should be placed on the street other than a car. Then, Masuyama got an idea to put his works on a truck and show them in a parking space. In Japan, drivers are only permitted to park along the street for an hour at the longest. If they park for more than an hour, they get a ticket for illegal parking with a fine and a penalty that negatively effects their possession of driver's licenses. Showing the work in a truck in a street was subjected to such a time limit and keeping the truck in a same spot was impossible due to an sensor in the parking meters.

In order to park the truck legally in the street, he had to move it from one space to another every single hour. These limitations urged Masuyama to create an exhibition called "legal parking" where he created a performance of moving a vehicle every hour. Creating a connection between the parking and the gallery, Masuyama conjured a scenario in which the gallery was a basement where a fictional task force was standing by. The task force has a mission to rescue good citizens from the police's enforcement against illegal parking. One of the purpose of this performance was to give the police the slip in order to achieve the legal occupation of the street under the name of an art exhibition.

The exhibition was held at the Gallery GEN located in an area where galleries were most densely clustered close together in Tokyo with street parking lots at the foot of the gallery buildings. An electric signboard in the gallery basement showed, in red numbers, the limits of the parking time. It counted how long he had until the time limit (60 minutes) would be up. When the counter showed zero, a siren began to wail and a "CAUTION" lamp started flashing. An emergency had arisen! The task force in the basement immediately went into action to rescue the truck from a police parking ticket.

This performance took place every hour as long as the exhibition lasted. The design for the invitation card for this project imitated a real parking ticket. All detailed props - from the signboard, the uniforms for the corps and their ID cards, to the promotion video introducing the corps and the performance itself - were thoroughly staged in a style of an action film. The reality of the performance succeeded despite such a fictional setting. Masuyama suceeded in creating a dynamic link between a space of fiction (a gallery) and a space of reality (a city).
Three days after the opening, the Ginza-Tsukiji-police approached Masuyama to stop such continuous use of the street. However, they were neither able to arrest him nor able to move the truck because the performance was completely legal. The only thing they could was to give the artist a warning. So Masuyama completed the 6 days of performance as he originally planned.

In order to create a visual relationship between the outside of the truck and the inside of the gallery, a sculpture of Masuyama was posed in the platform of the truck, mirroring an identical pose held by Masuyama himself inside the gallery, as if waiting to begin his mission. In the gallery Masuyama wore a guard costume. On the other hand, the sculpture of him was in a business suit, suggesting an ordinary office worker.