In a portable printer that uses a pulse motor for feeding a recording medium and includes a printing head that prints the recording medium, a printer controller that controls the printing head, and a pulse motor controller that controls the pulse motor, rest level setting information having rest levels and rest times set in correspondence to one another is previously stored, the elapsed time after a printing process is started is counted, the operating time of the pulse motor is counted, a rest level is determined based on the elapsed time after the printing process is started and the operating time of the pulse motor, a rest time is set by referring to the rest level setting information based on the determined rest level and a rest process is performed based on the thus set rest time.