An audio mixing device includes: an adder that adds a plurality of PDM signals each converted from a plurality of digital audio signals; a D/A converter that performs D/A conversion on a digital audio signal outputted from the adder and outputs an analog audio signal; and a synchronization device that is provided prior to the adder, and that synchronizes each of a plurality of digital signals with one another by use of the same predetermined synchronization timing signal and outputs each of them to the adder.