An in-vehicle air conditioning device includes a refrigerant circuit and a controller. The refrigerant circuit includes an electric compressor, a condenser, an expansion valve, and an evaporator. A refrigerant circulates through the refrigerant circuit. The refrigerant circuit includes a pipe which is connected to the electric compressor and through which the refrigerant discharged from the electric compressor flows. The controller calculates a pulsation frequency of pulsation generated in the pipe based on a target rotational speed for the electric compressor based on an air conditioning request. The controller calculates an air column resonance frequency of the pipe based on a sonic speed of the refrigerant and a length of the pipe. When the pulsation frequency is within a predetermined frequency band including the air column resonance frequency, the controller updates the target rotational speed for the electric compressor so as to avoid the pulsation frequency being within the frequency band.