To provide a method, etc., by which the radiation angle and radiation pattern of a semiconductor laser can be measured accurately.

A diffraction grating 10 is set up in an inclined state on this side of a light-receiving element 7 set up on the measurement axis X of the semiconductor laser 6 and a light-receiving element 9 for axial alignment is caused to receive the primary diffracted light of the grating 10. The laser 6 is set up on a rotary stage 5 which rotates around the measurement axis X and two-directional direct acting type stages 4, which can respectively move in orthogonal two directions in a vertical plane and the position of maximum light quantity at each rotational position is specified based on the output of the light receiving element 9, while the stages 5 and 4 are driven. Then, the grating 10 is removed from the measurement axis X, and the radiation angle of the laser 6 is found by measuring the light quantity of rotating the light- receiving element 7 to a relative position on a circular arc around a light- emitting point b, by making the center of the emitting pattern to coincide with the measurement axis X, by controlling the angle of rotation and position of the laser 6 based on the information on the position of maximum light quantity.