| abstract |
(57) [Object] To provide a thermal developing apparatus capable of performing low-cost and easy thermal stable development and stable gradation reproduction. A maximum heating value of a heater (32) is set to Hmax. Assuming that the heat capacity of the film F is M, 0.07 ≦ M / Hm a, the duty ratio does not become too small, the tone ratio can be controlled easily and stably, and the film F is heated by the relationship M / Hmax ≦ 0.75. Even if the amount of heat deprived of the film 32 fluctuates with time, the heater has a sufficient margin, the temperature of the film F is stabilized, the heat is sufficiently developed, and stable gradation reproduction can be performed. |