A variation detection device has a processor, an AD converter converting a signal voltage output from a sensor to generate an AD converted value and outputting the AD converted value to the processor, a temperature sensor detecting a temperature of the sensor, and a memory storing a table which indicates a relationship between temperatures and initial values. When receiving the AD converted value, the processor identifies a temperature of the sensor based on an output of the temperature sensor, reads out an initial value corresponding to the identified temperature from the table, and calculates a variation between the initial value and the AD converted value.