To provide a substrate co-fastening structure that can inexpensively detect a fastened state in co-fastening a substrate with another co-fastened component by a screw.

The substrate co-fastening structure co-fastens a second housing 42 between a head 32 of the screw 3 and the substrate 1 in fixing the substrate 1 mounted with an electrical component, to a first housing 41. A substrate land 12 electrically connected to the electrical component is formed around a screw insertion hole 11 of the substrate 1, and a detecting metal fitting 5 brought into contact with the head 32 of the screw 3 and the substrate land 12 with predetermined set load or more in the normally fastened state of the screw 3 is provided between the head 32 of the screw 3 and the substrate land 12. A current is thereby carried between the head 32 of the screw 3 and the electrical component, and the fastened state of the screw 3 can be determined based on the current carrying state.