PURPOSE: To prevent the submersion of the bed of a truck or the periphery thereof at the time of the delivery work of clinker from a clinker hopper or the dispersion of clinker, by efficiently excluding the moisture separated to the upper layer in the clinker hopper.

CONSTITUTION: The clinker 8 stored in a clinker hopper 7 separates water 9 above the clinker 8 and forms an upper layer to be stagnated. Moisture detectors 10a...10f and solenoid valves 11a...11f are arranged to the outer peripheral wall of the clinker hopper 7. Moisture detecting pockets 12a...12f are provided to the wall surface of the hopper in order to detect the moisture in the clinker 8 and a water level is detected. When a water level is present between water level lines A, B, the moisture detectors 10b, 10c detect moisture and an AND condition is formed to open the solenoid valve 11b to discharge water. When the water level falls and to moisture is detected by the moisture detector 10b, an NOT condition is formed to close the solenoid valve 11b. This operation is repeated and the water 9 of the upper layer in the clinker hopper is discharged.