PURPOSE: To keep the cleanness in a pass box same as high as that in a clean room, the cleanness level of which is higher, by a structure wherein openings for leading-in air and openings for discharging air are respectively provided on the wall surfaces of the pass box facing to the clean room, in which semiconductors are manufactured and the like.

CONSTITUTION: One or a plurality of openings 10 for leading-in air are provided on the wall surface on the clean room A side, the air pressure in which is higher than that in the exterior, of a box main body 1, while one or a plurality of openings 11 for discharging air are provided on the wall surface on the exterior B side, the air pressure in which is lower than that in the clean room A, of the box main body 1. Due to the difference between the pressure in the clean room A and that in the exterior B, the air passes from the clean room A kept at a high cleanness level at all times through the opening 10 for leading-in air, the interior of the box main body and the openings 11 for discharging air to the exterior B, the cleanness level in which is low. Consequently, the cleanness in a pass box can be kept at the same high cleanness level as that in the clean room A, resulting in enabling to prevent dusts and the like from entering the clean room A regardless of the opening and closing of the doors 2 and 3 of the pass box.