A printer capable of correctly sensing the internal ambient temperature of a printer body with no influence by an electronic component such as a power supply component reaching a high temperature is obtained. This printer comprises a temperature sensor chip for sensing the internal ambient temperature of the printer body, the electronic component and a ground pattern formed on a wiring board for grounding the temperature sensor chip and the electronic component. A portion of the ground pattern connected to the temperature sensor chip is partially formed narrower than another portion of the ground pattern connected to the electronic component.