An endless dough conveyor 16 is provided with a resin endless toothed belt 18 instead of a metal chain. A toothed pulley 22 around which the endless toothed belt is wound is also made of resin. A rail 64 is disposed adjacent to a horizontal path of the belt, and a roller 46 attached to the belt is adapted to roll on the rail. At least two induction motors are provided for driving the endless toothed belt. The induction motors are supplied with electric power from a single inverter 35. At least a pulley is provided with a detecting unit 80. The detecting unit 80 detects a state in which teeth of the endless toothed belt climb onto that of the pulley, thereby predicting breakage of the belt. Thus, it is possible to prevent contamination of dough in a proofer.