A print control device for a thermal printer for detecting a failure in a component of the thermal printer to prevent an incorrect printing of an item to be printed which provides for a thermal resistor associated with each component of the printer to render the printer inoperative when the component becomes defective, and a MOSFET for each thermal resistor associated with a feeder, a driver and a group detector which prevents the printer from printing when the thermal resistor changes the effective resistance in the circuit with the MOSFET and the group detector and driver.