Provided are a high-efficiency power conversion device and a variable-speed pumped-storage power generation system that can achieve long life span and improved reliability. A power conversion device includes a bypass switch connected in parallel to a frequency converter for performing AC-AC conversion including a converter for performing AC-DC conversion and a converter for performing DC-AC conversion. A control device of the frequency converter includes an AC current control unit (301) that controls an AC current flowing to the frequency converter, a DC current control unit (302) that controls a DC current flowing to the frequency converter, and a zero-phase current control unit (303) that controls a zero-phase current flowing to the bypass switch. The zero-phase current control unit (303) is operated when the bypass switch and the frequency converter are switched.