To improve operation efficiency without causing complication of constitution and an increase of cost.

A grain storage structure of a combine harvester is equipped with a grain unloading apparatus 7 composed by installing a bottom screw 10 arranged at the bottom of a grain tank 6, a vertical screw conveyor 11 for lifting the grains carried out from the grain tank 6 with the bottom screw 10 and an unloading screw conveyor 12 for unloading the grains from the vertical screw conveyor 11 to the outside of the machine. The grain storage structure of the combine harvester is further provided with a fill-up sensor 27 in the grain tank 6. A controlling means 30 for making the grain unloading apparatus 7 performs filling operation so as to fill the vertical screw conveyor 11 with the grains stored in the grain tank 6 based on the detection of the fill-up with the fill-up sensor 27.