In a search coil placed near the brush, the voltage is induced when the sparks occur under the brush. The peak value, the mean valve of the induced voltage and the frequency of occurrence of the voltage above a certain value are found well to indicate the nature of the spark by means of the high speed Brown tube oscillograph. A new spark indicator is devised which is consisted of the indicators of these three factors. The spark numbers which indicate the sparking order now under use sometimes are mislead, because there are several kinds of sparks even the spark numbers are the same. During the experiments of railway motors, we found there were at least two kinds of sparks quite different in nature. This indicator is a remote measuring devise and is fitted for the spark inspection where the motor is under floor as the railway motor. The results of the comparisons of the commutation faculty of the import-brush NCC-258 and the brushes made in Japan, show no special difference in the laboratory tests. The test results of the sparking of the high speed operation of the electric cars are also added.