A portable cellular phone is provided which is capable of minimizing a number of times of processes of reading user data from a user identity module (UIM) card and expansion of user data in an embedded memory when power is ON. The portable cellular phone is so configured that the UIM card can be mounted in its UIM card socket and, once the UIM card has been installed, a UIM card detached/attached history detecting unit detects whether or not the UIM card has been detached and then the UIM card or another UIM card has been attached and stores a result from the detecting in a register section embedded therein. Even when power is OFF state, the UIM card detached/attached history detecting unit can detect whether or not the UIM card has been detached and then attached again. After power is ON, a central processing unit (CPU) reads a register value stored in the UIM card detached/attached history detecting unit through a peripheral circuit. The CPU, only when having judged, based on the register value, that the UIM card has been detached, reads information containing user data such as a telephone number directory or a like from the UIM card and expands it in a random access memory (RAM).