PURPOSE: To easily cope with the variety, harvest, etc., of grains by providing a photosensor which detects grains fed out of a grain passage in an array so that its output is adjustable, and obtained its detection output in a stable maximum state.

CONSTITUTION: Grains thrown in a hopper 4 are fed out of the grain passage in an array and reach the photosensor while put in recesses 10 of a feed-out roll 6, and then the sensor 2 detects and outputs the degree of reflection. Then, a driving circuit operates to rotate an adjusting motor 13, and a comparing and amplifying circuit amplifies and compares the detection output. The result is outputted as a positive or negative signal and a control circuit turns the adjusting motor 13 forward or backward through a motor forward turning or motor backward turning circuit to move up and down the sensor 2. Then, when a maximum detection output is detected, a motor stopping circuit operates to stop the motor 13. Further, when a fitting plate 11 is detached, the sensor 2 can be taken out and maintenance inspection is easily performed.