PURPOSE: To make it possible to surely switch a port even at the time of receiving an input prime signal from a port other than an already set port prior to the start of all-port receiving processing.

CONSTITUTION: A printer device 1 connected to plural host equipments (hosts) 2, 3 is provided with a means for monitoring the input of an initializing signal and a port switching control circuit 6, and when printing information is not inputted for fixed time after inputting printing information from either one of the hosts 2, 3, the mode of the printer 1 is turned to an all-port receiving mode. Even at the time of inputting an input prime signal from a port other than a port to which data have been already inputted before turning the mode to the all-port receiving mode, the circuit 6 is driven and port switching can surely be executed in the all-port receiving mode.