A bullet supply port opening-closing device for a simulation gun which generates compressed air by operating a piston cylinder mechanism, blasts a bullet loaded in a barrel with the compressed air from an inter-nozzle , and shoots the bullet, the bullet supply port opening-closing device comprising: a nozzle base used as a communication member that causes the inter-nozzle to retract in response to an operation of a movable portion of the piston cylinder mechanism and transmits the operation of the movable portion to the inter-nozzle in order to open a bullet supply port leading to a space in front of the inter-nozzle , wherein the communication member is constituted by a nozzle side part (29-1) and a movable portion side part (29-2), the bullet supply port opening-closing device further comprising an engagement mechanism , wherein the nozzle side part (29-1) and the movable portion side part (29-2) are configured to be able to be engaged with and disengaged from each other by said engagement mechanism such that the nozzle side part (29-1) and the movable portion side part (29-2) retract together so as to open the bullet supply port , after the nozzle side part (29-1) is isolated from the movable portion side part (29-2) which continues to retract, an open state is retained for a certain time, and the movable portion side part (29-2) advances so as to be engaged with the nozzle side part (29-1), characterized in that the engagement mechanism is configured to include an engagement portion provided in the nozzle side part (29-1) and a disengagement portion provided on a gun main body side, and that the engagement portion has a pivot and is rotatably and pivotally supported by the pivot in the movable portion side part (29-2). a nozzle base used as a communication member that causes the inter-nozzle to retract in response to an operation of a movable portion of the piston cylinder mechanism and transmits the operation of the movable portion to the inter-nozzle in order to open a bullet supply port leading to a space in front of the inter-nozzle , wherein the communication member is constituted by a nozzle side part (29-1) and a movable portion side part (29-2), the bullet supply port opening-closing device further comprising an engagement mechanism , wherein the nozzle side part (29-1) and the movable portion side part (29-2) are configured to be able to be engaged with and disengaged from each other by said engagement mechanism such that the nozzle side part (29-1) and the movable portion side part (29-2) retract together so as to open the bullet supply port , after the nozzle side part (29-1) is isolated from the movable portion side part (29-2) which continues to retract, an open state is retained for a certain time, and the movable portion side part (29-2) advances so as to be engaged with the nozzle side part (29-1), characterized in that the engagement mechanism is configured to include an engagement portion provided in the nozzle side part (29-1) and a disengagement portion provided on a gun main body side, and that the engagement portion has a pivot and is rotatably and pivotally supported by the pivot in the movable portion side part (29-2). <EOS>