A heat treatment apparatus for making a heat treatment while estimating temperatures of objects-to-be-processed that can estimate correct temperatures of the objects-to-be-processed. A reaction tube includes heaters and temperature sensors, and receives a wafer boat. A controller estimates temperatures of wafers and temperatures of the temperature sensors in zones in the reaction tube corresponding to the heaters by using the temperature sensors and electric powers of the heaters. Based on relationships between estimated temperatures of the temperature sensors and really metered temperatures, functions expressing the relationships between the estimated temperatures and the really metered temperatures are given for the respective zones. The functions are substituted by the estimated wafer temperatures to correct the estimated wafer temperatures. Electric powers to be fed to the respective heaters are respectively controlled so that the corrected wafer temperatures are converged to target temperature trajectories.