In a mass spectrometer, due to impurities accumulated inside a frame, a withstand voltage may decrease, and electric discharge may occur in an ion source, thereby making it impossible to perform normal measurement. Since the result of abnormality measurement due to the electric discharge cannot be distinguished from measurement abnormality caused by clogging of a tube between a pretreatment part and a needle, there is a problem in that time is required to identify abnormal portions, and a maintenance property is lowered. As a means for solving the problem, the present invention comprises: a return current detection unit connected in series between a frame and an ion source power supply that applies a voltage to the needle; and a return current detection unit that is connected in series between the frame and a counter electrode power supply that applies a voltage to a counter electrode. By comparing a current measured by the return current detection unit with a predetermined threshold value, the occurrence of the electric discharge and the location where the electric discharge occurs are detected.