PURPOSE: To provide the parameter deciding method of a temperature control in which a parameter for reaching a set temperature in a short time without any overshoot can be decided.

CONSTITUTION: In a control system in which a deviation to the set temperature and the change rate of the deviation are inputted, and the output rate of a heater is controlled, at the time of defining the temperature of a point of time tcut when the first state of a manipulated variable 100% at the time of an auto- tuning is turned to the state of a manipulated variable 0% as Tcut, and defining a peak temperature value (overshoot value) which an object to be controlled reaches at that time as Tpeak, the object to be controlled is approximated by a secondary delay system, a relation between the above mentioned Tcut and Tpeak is searched, and the control parameter is calculated from the relation.