Provided is an optical receptacle (140) having an installation plane (141), an optical plane, and a reference plane (147). An inclination angle of the reference plane (147) with respect to the installation plane (141) is smaller than an inclination angle of the optical plane with respect to the installation plane (141). Then, a first inclination angle θ1 that is the inclination angle of the reference plane (147) with respect to the installation plane (141) and a second inclination angle θ2 that is an inclination angle of the optical plane with respect to the reference plane (147) are measured. Then, the first inclination angle θ1 is added to the second inclination angle θ2 to calculate a third inclination angle θ3 that is the inclination angle of the optical plane with respect to the installation plane (141).