To provide the heat treating device and method of an object to be treated capable of improving the follow-up performance and stationary characteristics of control.

This heat treating device of an object to be treated is provided with a heat treating furnace 4 for performing the heat treatment of an object to be treated, a sequencer 10 for outputting plural set values and plural control part selection signals for controlling the heat treating furnace, and plural control system loops constituted for controlling the plural controlled variables of the heat treating furnace, and each control system loop is provided with plural control parts for outputting manipulated variables based on the set values from the sequencer 10 and the controlled variables from the heat treating furnace and switchers 3-1, 3-2 and 3-3 for selecting one of the manipulated variables outputted form the plural control parts according to the control part selection signals from the sequencer 10, and for outputting it to the heat treating furnace 4. In this case, the sequencer 10 is provided with a means for independently operating the switching of the control constitution of the plural control system loops.