PURPOSE: To automize a test of board of a mask ROM, by preparing a memory cell stored with a code corresponding to a test program on a semiconductor substrate.

CONSTITUTION: In the 2nd memory cell group 2, information representing a code determined in response to the content of information stored in the 1st memory cell group 1 is written with a mask ROM the same as the 1st memory cell group. A test pad 6 on the semiconductor substrate is connected to memory cells 21W28 constituting the 2nd memory cell group 2 and gate transistors 31W38 via an input buffer 7. After the information representing a code is read out, signals Q and Q' are inverted, the 2nd memory cell group 2 is all made nonconductive, the 1st memory cell group 1 is connected to sense amplifiers 41W48 to make readout possible.