A CAES power generation device includes: a compressor/expander combined machine that is of displacement type and has a function as a compressor for compressing air and a function as an expander for expanding compressed air; a motor/generator combined machine that is mechanically connected to the compressor/expander combined machine and has a function as an electric motor for driving the compressor/expander combined machine and a function as a generator driven by the compressor/expander combined machine; and a pressure accumulation tank that is fluidly connected to the compressor/expander combined machine and stores compressed air generated by the compressor/expander combined machine.