To provide a pellet fuel combustion system in which a pellet fuel is easily supplied to a fuel tank, the temperature of the fuel does not become high, and the fuel can be stably supplied from the fuel tank to a combustor in a combustion chamber.

The pellet fuel combustion system 1 has the fuel tank 4 below the combustion chamber 2 where the combustor 3 is placed in the lower part. The pellet fuel in the fuel tank is supplied to an inlet port 5a of a carrier pipe 51 of a screw conveyer 5 while being mixed by a mixing member 42, and transmitted from the lower part of the tank to the part above the combustor 3 by a screw 52 in the pipe 5. The pellet fuel is then passed to a fuel supply path 54 at an outlet port 51b located just below the upper end of the pipe 51 to be slid down through the supply path 54. The fuel then falls down from the front end 54a of the supply path located above the combustor 3, thereby supplying the fuel to the combustor.