PURPOSE: To provide a program system interface circuit which can simplify the constitution of a sub-board connected to a mother board selectively and simplify the constitution of a connector to connect the mother board and the sub-board.

CONSTITUTION: Respective sub-boards B1 and B2 respectively store the pin arrangement of self-connectors C1 and C2 into memories M1 and M2. By a programmable device PD inserted between a connector C0 and a circuit K0, a mother board B0 reads the information concerning the pin arrangement from the memories M1 and M2 of the sub-boards B1 and B2 through the connector C0, and changes the pin arrangement of the mother board B0 so as to be applicable to the pin arrangement. Thus, there is the effect that by the number of pins to an irreducible minimum, the sub-board of the different pin arrangement can be connected.