To manufacture a precast concrete block continuously different in length by the same form apparatus while holding the precision of an end part structure necessary for unevenness meshing and bolt clamping.

The length between both side surface forms (5) is continuously changed by moving a movable edge face form (1) to set the same to an arbitrary position. A protruded part becoming the obstruction of the movement of the movable edge face form (1) after the filling with concrete is attached as a form accessory part (2) and constituted so as to be detached upward after concrete is cast. Concrete is charged by adding force to the side surface and upper surface of the moving edge face form (1) from a movable frame (11) or a fixed frame (14) independent of a form supporting device to ensure the precision of the end part structure.