To automatically correct time of a clock and to always keep accurate time information without increasing running costs by acquiring time information showing the log-in or log-out time from information sent from a host computer.

A personal computer 1 executes processing of a personal computer communication program 132 and performs a log-in processing for commercial service to a host computer, a data transfer processing and a log-out processing. A time information acquisition program 133 takes information on a log-out date and time out of a log-out message received from the host computer and also acquires information on the current date and time from a clock 16 to store information in a prescribed variable. A time information storage program 134 records log-out time information and time information on the built-in clock 16 of the computer 1 in a record file. Then a time correction program 135 secures coincidence between time information on the clock 16 and log-out time information to correct time errors.