Disclosed is a heating power adjusting apparatus of a hot blast heater which controls pressure of air supplied to a burner by executing selectively switching between the cross-sectional areas of orifices in a flow space of air located between a pump and a burner head, and thereby variably adjusts heating power generated from the burner. The heating power adjusting apparatus adjusts includes a valve body including an air injection part, an air exhaust part, and an air flow space between the air injection part and the air exhaust part, an orifice body rotatably installed in the air flow space of the valve body and provided with a plurality of orifices having different flow cross-sectional areas to variably adjust the flow rate of air, and a rotary knob to adjust rotation of the orifice body with respect to the valve body.