To provide a water adding device in which the water and sand can efficiently be mixed.

This device is constituted of a conveyor 16 for carring the sand, a vessel 30 in which the inlet is positioned at the lower end of the discharging end of the conveyor 16 and a vertical path for sand flow is formed between the discharging end and the inlet of the conveyor, a mixer 40 having a rotating shaft 42 penetrating a part of the vessel 30 and a first and a second nozzle sets 22 directed to the vertical path for sand flow. The water is sprayed to both sides of the sand flow dropped along the vertical path with the nozzles and the sand sprayed with water is mixed in the vessel 30.