Water-temperature sensors for detection of temperature of cooling water 12 having passed through an engine 1 are increased in number into two (18 and 19). A controller 20 is provided to confirm that each of detection values of the water-temperature sensors 18 and 19 is within a normal range and then employ either of the detection values as temperature of the cooling water 12. The controller 20 is configured such that, when either of the detection values of the water-temperature sensors 18 and 19 is out of the normal range, the remaining detection value within the normal range is employed as temperature of the cooling water 12.
