A high-voltage unit casing 10 for on-vehicle use to house therein a plurality of devices includes: a first side face 20; a second side face 21 opposed to the first side face; and a connecting portion 22 for structurally connecting the first side face and the second side face to each other. The connecting portion includes a partitioning portion 50 which is fixed to the first side face at a fixing portion and which extends from the fixing portion toward the second side face, the partitioning portion being located at a position separate from an upper surface and a lower surface of the high-voltage unit casing in an inner surface of the first side face. Spaces for placing at least one device included in the plurality of devices are formed on both upper and lower sides, respectively, of the partitioning portion.