To suppress deformation of a portion to be clamped even when a load applied to the portion to be clamped is increased at the time of fixing a front opening unified pod (FOUP), a clamping arm pivotable between a retracting position and a clamping position about a rotational axis inclined relative to a bottom surface of the FOUP is arranged. The clamping arm is housed in a housing depression so that the clamping arm at the retracting position is situated below a surface of a mount base, and at the clamping position, protrudes from the surface of the mount base and becomes engageable with the portion to be clamped.