A position regulation member, provided in one of a base unit and a removable unit that is attached to the base unit in a removable state, that positions the removable unit relative to the base unit, the positions regulation member including a position regulation arm provided so as to be mobile between a first position and a second position through the use of a cam mechanism, and a biasing spring attached to the position regulation arm. When the position regulation arm is moved from the first position to the second position or from the second position to the first position, the biasing spring biases the position regulation arm in the direction of the movement of the position regulation arm by first elastically deforming and then switch the direction of biasing by passing a inversion point.