Abstract: A fail-safe device for an engine temperature sensor. A value of the engine temperature detected by the engine temperature sensor is renewed and stored for engine control. While the engine is detected to be in a low temperature region lower than a predetermined value on the basis of the detected value, renewal of the detected value is inhibited when it has decreased. It is determined that the detected value has decreased, when the detected value is lower than a lower limit value. The lower limit value is set to a value corresponding to the detected value when the engine is detected to be in the low temperature region, whereas it is set to the predetermined value when the engine is detected not to be in the low temperature region. Renewal of the detected value is inhibited when the detected value has not remained within a predetermined range over a predetermined time period.