One aspect of the invention provides a substrate position detecting method for charged particle beam photolithography apparatus in order to be able to measure accurately and simply a substrate position on a stage. The substrate position detecting method for charged particle beam photolithography apparatus includes placing a substrate on a stage that can be moved in an X-direction and a Y-direction; measuring a position in the X-direction of the stage while moving the stage in the X-direction, and illuminating obliquely an upper surface of the substrate with a laser beam to receive light reflected from the substrate with a position sensing device; computing a barycentric position of the reflected light when the stage is moved in the X-direction; measuring a position in the Y-direction of the stage while moving the stage in the Y-direction, and illuminating obliquely the upper surface of the substrate with the laser beam to receive light reflected from the substrate with the position sensing device; computing a barycentric position of the reflected light when the stage is moved in the Y-direction; and computing the positions of the substrate from the position measurement results of the stage and the computed barycentric position.