The present disclosure relates to a monitoring system for a plurality of power devices serially connected in a main circuit of a current transmission path comprising a first power device and a second power device each including a semiconductor element; a first sensor connected to the first and second power devices, and which senses information related to a first current flowing in the first power device; a second sensor for sensing information related to a second current flowing in the second power device; a third sensor for sensing information related to a third current flowing between the first power device and the second power device; and a control unit for comparing the first current and the second current on the basis of the third current measured by the third sensor, and determining whether the state of each power device is abnormal based on a difference with the third current.