Structure for an electronic keyboard instrument includes upper and lower cases. The lower case has a bottom plate having lower slits, and the upper case has an upper plate having upper slits. The upper and lower cases are fastened together with the upper case overlapped on the lower case and with opposite edge portions of a circuit board inserted in the lower and upper slits in such a manner that the circuit board is disposed upright between the upper and lower cases. Heat radiating plate is attached to the circuit board. A wiring, drawn out from an operation section provided on the upper case, is wired to pass across a neighborhood of the upper end surface of the heat radiating plate under the lower surface of the upper plate. Heat blocking plate is provided between the heat radiating plate and the wiring to block transfer of heat from the heat radiating plate to the wiring.