To accurately detect the weight of accumulated powder or the particle surface level within a powder storage tank by installing a conductive structure having a contact surface against which the specified ratio or more of the total number of powder particles put in from a powder supply opening strike within the storage tank.

A conical conductive metal structure 3 is installed so as to face in the putting direction of powder supplied from a powder supply opening 2 in a storage tank 1, and earthed through a lead wire 5. In the constitution of the powder storage tank 1, 50% or more of the total number of the powder particles supplied from the powder supply opening 2 strike against the conical contact surface of the conductive structure 3 and are accumulated, and in this striking, static electricity charged is removed. A load cell 4 can accurately measure the state of accumulated powder without being affected by static electricity.