To provide a RAM value monitoring device for a plurality of microcomputers saving space and low in developing cost.

Programs 35 to be executed by a PC (personal computer) 30 for transmitting an instruction according to the operation of a user are two same programs to be started in parallel in a device 5 in which RAM value measuring equipment 40 connected to equipment 10 having microcomputers 1 and 2 performs a processing to take out RAM values from the microcomputers 1 and 2 according to an instruction transmitted from a RS232C port of the PC 30. In a communication driver of the program 35, a process P1 started earlier is changed into one for the microcomputer 1, a handle of the RS232C port is acquired from OS (Windows: trademark) of the PC 30, and the handle is copied for a process P2 started later. The process P2 is changed into one for the microcomputer 2 and performs communication with the equipment 40 by using the copied handle.