PURPOSE: To provide a control device for an air-conditioning device having an electric heater, which can carry out efficient heating and power saving.

CONSTITUTION: There are provided an evaporator 8, an electrical heater 12, a heat-pump type refrigerating circuit 1 and an electronic control means 3. The control means 3 is composed of an electronic control unit 30, a compressor drive part 31 and an electrical heater drive part 32. The unit 30 computes an optimum heating capacity Qcmax for a refrigerating circuit 1 with which a required heating capacity QT and a total efficiency COPT becomes maximum. When QT is larger than Qcmax, the rotational speed of a compressor 4 is determined so that the heating capacity Qc of the refrigerating circuit 1 becomes Qcmax, and further, an energizing value for the heater is determined so that heating capacity QE of the heater becomes QT-Qxmax. Meanwhile, when At is smaller than Qmax, the rotational speed of the compressor is determined so that Qc becomes QT, and further, the energizing value for the heater is set to zero.