To invariably give a comfortable cooling/heating feeling to a driver regardless of the work state and work duration.

An arithmetic device 30 feeds the signal from a forward/reverse operation lever 52 to a detection part, and a counting part judges whether the signal is fed four times or more in one minute or not. When this judgment is satisfied, the arithmetic device 30 judges that the work is a heavy work, and an output part outputs the drive voltage signal to a relay 31. The relay 31 is excited, a wire 57 conducts, and the electrical signal indicating the zero resistance θ is fed to an air conditioner controller 11 regardless of the setting of a variable resistor 12. The temperature setting of a cooler is controlled to the lowest temperature by the air conditioner controller 11.