To ensure proper linkage with a next process and accuracy in production plan by properly determining a time between heat treatment times.

This method of determining the time between heat treatments, between a first heat treatment process and a second heat treatment process following the first heat treatment process, in a batch-type heat treatment furnace in which heat treatment and cooling between the heat treatments are performed by loading a workpiece on a carriage and taking in and out the same to the furnace, includes a step for applying a value obtained by dividing the difference between a start temperature and a termination temperature by a furnace cooling speed predetermined according to a size of the furnace, as a carriage cooling time, when the start temperature of the second heat treatment process is higher than the termination temperature of the first heat treatment process, and setting the carriage cooling time to 0, when the start temperature of the second heat treatment process is lower the termination temperature of the first heat treatment process, and a step for determining the sum of the carriage cooling time and a loading time to the carriage as the time between heat treatments, when the carriage cooling time is longer than an additional time predetermined according to a workpiece cooling method, and determining the sum of the additional time and the loading time as the time between heat treatments, when the carriage cooling time is shorter than the additional time.