PURPOSE: To reduce the power consumption, by applying the starting to the power supply of a printer unit when a data is accepted from a central processor and then actuating the printer unit and its power supply only in the print mode.

CONSTITUTION: When a switch S1 is applied, a power supply circuit PC2 works to make a data control unit CU1 be ready for working. Then the data is transmitted from a central processor via a transmission line L. This transmission of data is detected by a controller CU2, and a contact S2 of a relay RY is closed. Thus a power supply circuit PC1 of a printer unit PU2 works to print the data. When the printing is over, the controller CU2 opens the contact S2 to stop the working of the circuit PC1. In such way, the printer unit and its power supply are made active only in the print mode to reuce the amount of power consumption.