Flux concentration cores that encircle bus bars are arranged at different heights. When viewed from an extending direction (a Z-direction) of the bus bars, the first flux concentration core and the second flux concentration core that are adjacent to one another partially overlap each other, and the second flux concentration core and the third flux concentration core that are adjacent to each other partially overlap each other. Therefore, the flux concentration cores are able to be arranged around the bus bars even when the spaces between the bus bars are narrow.