PURPOSE: To prevent the leakage of the secrecy held in a built-in memory by inhibiting fixedly the data reading actions of the built-in memory in response to the conductive or non-conductive state between the prescribed one of a power supply lead of a conduction pattern connected to an electrode pad of a chip and a memory.

CONSTITUTION: A single chip type microcomputer 1 has such a constitution where an operation to read the data out of a built-in memory 5 and to send them to an internal bus is fixedly inhibited in response to the conductive or non-conductive state between a memory and the prescribed one of a power supply lead 39 or a conduction pattern connected to an electrode pad Vdd1 of a chip. Thus it is possible to prevent such a defective case where the secrecy of the specific information on the software, etc., stored in a built-in memory of a mask ROM, etc., despite the set-up of a test mode to open an internal bus to the outside or an action mode to attain an access even to a built-in ROM when the microcomputer 1 serves as a general-purpose microcomputer containing no internal bus.