To reduce restrictions on wiring layout when a circuit for sensing the inflow of a current is provided on a substrate.

On the surface of an insulated substrate 30, there are a wiring pattern area 30a where a copper foil 32 is formed and non-wiring pattern areas 30b, 30b' where a wiring pattern is not formed, that is, the copper foil 32 is not bonded. A thermistor So for detecting the surface temperature of the copper foil 32 is disposed in the non-wiring pattern area 30b' on the surface in non-contact with the copper foil 32 and is electrically connected with the wiring pattern formed on the backside.