To prevent a lower end of a blocking body formed of a flexible material to open/close an opening part of a gantry-type car washing machine body from being lifted off by strong wind when the lower end is at a lower limit position.

A blocking body opening/closing device comprises stopped members provided on right and left ends of a lower part of a blocking body 25, a limiting member 37 to be engaged with the stopped member so as to limit the rise of the stopped member 141, and an elevating/lowering means which elevates the limiting member when a roller is rotated in the winding direction of the blocking body and lowers the limiting member when the roller 24 is rotated in the delivering direction of the blocking body. When the lower end of the blocking body is at the lower limit position, the limiting member is also held at the lower limit position to limit the rise of the stopped member. When the lower end of the blocking body is located above the lower limit position, the lower limit of the blocking body is permitted to be hung by a weight member 29, and when the lowering speed of the lower end of the blocking body is delayed than a preset value, the elevating/lowering speed of the limiting member and the rotational speed of the roller, and the relative position of the limiting member to the stopped member are set so as to press down the stopped member.