To provide a hydraulic retarder device of a crane truck switch increases the braking force in downhill running.

This crane truck is composed to mount a crane which operated by receiving a pressure oil from a hydraulic pump 4 driven by an engine 1. In this case, a clutch 5 is provided between the hydraulic pump 4 and the engine 1, and at the same time, pressure loss means 10, 20, 23, 24, and 25 are provided at the discharge side of the hydraulic pump 4, and furthermore, interruption change-over means 10, 31, 32, and 30 to turn ON and OFF the clutch 5 are provided.