To discriminate a high-output semiconductor laser element having a long service life by finding the COD levels of laser elements to be tested from the maximum outputs of the elements based on the COD level characteristics of the elements.

When the light output versus operating current characteristics of laser elements to be tested are measured at an ambient temperature of 70°C, the light outputs of the elements are saturated at about 400 mW. The maximum outputs of the elements at the ambient temperature of 70°C can be measured without destroying the COD levels of the elements by measuring the maximum outputs of the elements at the ambient temperature of 70°C, because the relations between the maximum outputs of the elements at the ambient temperature 70°C and the COD levels of the elements at another ambient temperature of 25°C are fixed. Therefore, a semiconductor laser element having a long service life can be discriminated by sorting out such laser elements that have relatively low COD levels based on the COD levels of the elements found by using the graph.