PURPOSE: To provide an under-pressure feeding device for the powder/grain which can suppress the air stream abrasion of a transport valve and prolong the life of the transport valve.

CONSTITUTION: An auxiliary transport valve 28 is installed on the outlet side of a transport pipe 24 in the vicinity of a transport valve 26 installed in the transport pipe 24 which communicates to the outlet of a pressurizing tank 22. Accordingly, when the inside of the pressurizing tank 22 is pressurized by the compressed air, the compressed air which leaks from the gap generated by the sliding abrasion between the valve body and the valve seat of the transport valve 26 is cut off by the auxiliary transport valve 28, and the pressure in the transport pipe 24 between the transport valve 26 and the auxiliary transport valve 28 increases. Accordingly, the pressure difference before and behind the transport valve 26 becomes zero, and the air leak of the transport valve 26 is eliminated, and the air stream vibration of the transport valve 26 can be prevented.