In a position closest to the mounting position of a microcomputer in a casing of a hybrid integrated circuit device on which is mounted the microcomputer and its peripheral circuit elements, an insertion hole is formed for a non-volatile memory which feeds data to the microcomputer. A socket for connecting the non-volatile memory is provided at the bottom of this insertion hole. Because of this configuration it is possible to connect the microcomputer and the non-volatile memory at an extremely short distance and the mounting efficiency of the integrated circuit device is increased. In addition, the non-volatile memory can detachably be mounted. Furthermore, the external shape of the insertion hole for the non-volatile memory is essentially the same as the external shape of the non-volatile memory so that when the non-volatile memory is inserted, the entire surface of this hybrid integrated circuit device is almost flat, providing excellent handling characteristics.