To provide an ashing treatment apparatus used in ashing treatment being pretreatment operation at the time of analysis of medicines and food, facilitating high temperature heating, capable of keeping an arbitrary set temperature stable and capable of preparing a large amount of a sample at once.

In the ashing treatment apparatus, an electric heater (6) is arranged on the inner bottom of a heat-resistant outer container 8 of which the bottom surface and side surface comprise a heat insulating material (7), and a heating plate (4) heated by the heater (6) through a space A (5) is provided above the heater (6) while a top plate (2) is provided on the heating plate (4) at a position lower than the height of an ashing container (1). A hole of which the shape is almost equal to the outer shape of the ashing container (1) is bored in the top plate, so that a space B (3) becomes near to a hermetically closed state when the ashing container (1) is inserted and the surface temperature setting mechanism of the heating plate (4) is provided.