To provide the subject instrument enabling the flow and the extent of accumulation of grains to and in a grain tank 27 to be understood easily.

This instrument 44 has such a scheme that the end portion 40 of a discharge cylinder 28 is faced on the upper part of a grain tank 27 in a threshing device such as on a combine harvester and grains pushed up by the screw conveyor 28a inside the discharge cylinder 28 are discharged by the aid of a rotary impeller 42 provided on the discharge end portion 40 into the grain tank 21; wherein an electric motor 43 connected to the rotary impeller 42 is controlled so as to be subjected to rotary drive at a given rate of rotation irrespective of the flow level of the above grains (granular to-be-treated object), and computer operations are made for determining the flow of the grains based on the measurement of the power consumption of the electric motor 43 and for determining the accumulation of the grains in the grain tank 27 based on the result of calculating cumulative power consumption.