A wiring device comprises a first printed wiring board and a housing for housing the first printed wiring board. The housing comprises a body and a cover that are coupled with each other while the first printed wiring board is held therebetween in a thickness direction of the first printed wiring board. The cover has engagement projections that are configured to be capable of being engaged with engagement recesses of the body. The engagement projections are configured not to be engaged with the engagement recesses in an incorrect direction that is turned by 180 degrees from a correct assembling direction around an axis parallel to the thickness direction of the first printed wiring board. Therefore, it is possible to prevent incorrect assembly, such as attaching the cover to the body in the incorrect direction as above.
