A printer apparatus terminates printing and discharges paper when an interface is disconnected during a printing process, whereby the next print data is received and is appropriately printed. In particular, when a printer apparatus that selectively uses a plurality of interfaces to receive print data from one of plurality of host units so that the print data can be printed by a single printing mechanism has an error such as interface disconnection during a process for printing print data received via the selected interface, the printer apparatus terminates the printing and discharges paper, whereby when print data is received via another interface and is printed, the printing can be smoothly performed without requiring the user to perform any operation.