A deteriorated section identifying unit refers to correspondence information that defines a deteriorated section of a plurality of bonding sections to the emitter electrode surface to which the first bonding wires are connected, for a combination of temporal change of a first voltage that is a difference between a potential at a collector main terminal and a potential at the emitter main terminal and temporal change of a second voltage that is a difference between a potential at the emitter reference terminal and a potential at the emitter main terminal, and identifies the deteriorated section corresponding to a combination of temporal change of the first voltage measured by a first voltage measuring circuit and temporal change of the second voltage measured by a second voltage measuring circuit.