A memory pack is provided having a random access memory connected between a positive power source terminal and a ground terminal, an addressing terminal coupled with the random access memory, and a data input/output terminal coupled with the random access memory. The memory pack further includes an LED energizing terminal, a light emission element which is connected between the LED energizing terminal and a positive power source terminal, the LED being lit by an energizing signal applied to the LED energizing terminal, a RAM energizing terminal and a photocoupler which is connected between the RAM energizing terminal and the random access memory and which responds to an energizing signal applied to the RAM energizing terminal to apply an output signal to the random access memory thereby to set the random access memory to be operative.