According to one embodiment, a substrate unit of the present invention comprises a first substrate, a second substrate and a coupling member. The first substrate has a first substrate main body and a circuit component. The second substrate has a second substrate main body, an opening portion provided at the second substrate main body, and a cooling module which cools the circuit component. The circuit component is mounted on a face of the first substrate main body which is opposite to the second substrate. The cooling module has a main body and a projecting portion. The coupling member fixes the main body to a second face of the second substrate main body, and couples the first substrate and the second substrate so as to fit the projecting portion in the opening portion and press the projecting portion against the circuit component.