A position measurement method includes, acquiring a sensing position of a distal end of a reference tool, measuring and acquiring a position of a machined surface, The method further includes measuring a position of a reference block disposed on a side of the tool sensor and calculating a relative position of the reference block to the sensing position from the sensing position and the position of the reference block, mounting the position measurement sensor to the main spindle and measuring a position of the reference block, calculating a length direction correction value of the position measurement sensor from the position of the reference block measured in the mounting of the position measurement sensor and the relative position, and measuring the object by the position measurement sensor and correcting a measurement position of the object.