To provide a load port which can move a mounted cassette to a predetermined removing reference position to be aligned, and can return the cassette back to original mounting position from the removing reference position, and to provide a method for adjusting the cassette position of a load port.

A mounting portion 30 includes a base stage 31 installed at a predetermined position on a horizontal plane, a floating stage 32 having a plane for mounting a cassette 50, and a position adjustment mechanism 33, wherein the position adjustment mechanism 33 moves the cassette 50, along with the floating stage 32, to the reference position of the cassette 50 for the base stage 31 in a preset x-direction and a y-direction, based on the size of the cassette 50.