PURPOSE: To improve the communication speed by controlling an action timing so that a serial parallel converting means and a parallel serial converting means in an interface selected at the time of selecting with an interface selecting means can be the action completing condition.

CONSTITUTION: Control means 14 and 17 control an action timing so that a serial parallel converting means 15 in the interface selected when an address signal, in which an interface selecting means 2 selects the interface is outputted can be the condition to complete the action to convert the serial data from a terminal to the parallel data of a prescribed bit and a parallel serial converting means 16 can be the condition in which the existing data are all made serial and transmitted to the terminal. For this reason, when an interface control means selects the interface, the selected interface can immediately transmit and receive the data with a time slot for the interface and the time to wait for the self-time slot is eliminated. Thus, the communication speed is improved.