A sheet storage apparatus includes an apparatus body, a sheet storage portion attachable/detachable to/from the apparatus body, a regulating portion to regulate a position of an end portion of the sheet stored in the storage portion, a cam member slidably movable by interlocking with a movement of the regulating portion, and a slide member supported on the apparatus body and slidably movable by engaging with the cam member in a case where the storage portion is attached to the apparatus body. A sensor includes a moving portion supported on the apparatus body and movable by engaging with the slide member, and a variable resistor, supported on the apparatus body, whose resistance value varies in response to a position of the moving portion in the second direction. The sensor outputs a detection value that varies in response to the resistance value of the variable resistor.