In a sensor signal processing apparatus, a control unit executes at least one of a temperature measurement process and a calculation process in parallel with a signal conversion process. In the temperature measurement process, the control unit causes a second A/D converter to execute the A/D conversion of a temperature signal. In the calculation process, the control unit calculates an offset and a conversion gain of a first A/D converter base on an A/D conversion value output from the second A/D converter and pre-prepared temperature characteristic data of a physical quantity sensor. In the signal conversion process, the control unit sets the calculated offset and the calculated conversion gain to the first A/D converter, and causes the first A/D converter to execute the A/D conversion of the sensor signal.