PURPOSE: To keep the temperature increasing rate constant even by changing the amount of bread dough stored in a storage chamber by measuring the temperature change in a storage chamber with lapsed time and controlling a heating means in such a manner as to keep a prescribed temperature increasing rate until the temperature in the chamber reaches a preset level.

CONSTITUTION: An openable door 8 is attached to the front face of a storage chamber 1, plural shelves 9 for holding bread dough are placed in the chamber 1 and air-ducts 10, 11 are formed at the upper part and the right and left sides in the chamber. An evaporator 3 and an electric heater 7 are placed in one of the side air-ducts and the temperature in the storage chamber is detected by a thermistor 14. The temperature in the chamber is compared with the lapsed time by a controller and the electric heater is controlled to keep a prescribed temperature increasing rate until the temperature in the chamber reaches a preset level.