To provide a warm air heater which uniformly, evenly and stably burns solid fuel using the movement of a fire grate itself as a means for averaging the thickness of a layer of the solid fuel on the fire grate so that the combustion of the solid fuel can be easily unified.

This warm air heater (W) includes a combustion furnace (1), a solid fuel supply machine (2), an air blower (30) for supplying the air to an air distribution passage (3) formed separately from the combustion furnace (1) along the combustion furnace (1), the fire grate (4) driven to be vertically moved and declined to a downstream side, a combustion air supply means (5) for supplying the air from a lower part of the fire grate (4), a spray air supply unit (6) disposed at a lower part of the supply port (21) of the solid fuel supply machine (2) and injecting the air toward the downstream side of the fire grate (4) to scatter part of the solid fuel, a burner (7) for igniting the solid fuel on the fire grate (4), and a heat exchanger (8) for exchanging heat between the air distributed from the air blower (30) and a combustion gas.