A heat treatment apparatus including: a processing container for processing wafers held in a boat; heaters for heating the processing container; and a control section for controlling the heaters. Heater temperature sensors are provided between the heaters and the processing container, in-container temperature sensors are provided in the processing container, and movable temperature sensors are provided in the boat. The temperature sensors are connected to a temperature estimation section. The temperature estimation section selects two of the three types of temperature sensors, e.g. the movable temperature sensors and the in-container temperature sensors, and determines the temperature of a wafer according to the following formula: T=T1×(1−α)+T2×α, α>1, where T1 and T2 represent detection temperatures of the selected temperature sensors, and α represents a mixing ratio.