The passage from a cooling medium inlet to a cooling medium outlet of a cooler includes: an upstream cooling portion and a downstream cooling portion for cooling heat generating bodies; an upstream distribution portion located on the cooling medium inlet side; a downstream distribution portion located on the cooling medium outlet side; a connecting portion for connecting the upstream cooling portion and the downstream cooling portion; and a partition portion for partitioning the upstream cooling portion and the downstream cooling portion, and the upstream distribution portion and the downstream distribution portion. The passage is connected so that the cooling medium flows in order of the upstream distribution portion, the upstream cooling portion, the connecting portion, the downstream cooling portion, and the downstream distribution portion.