Series-connected multi-level power conversion device

A series-connected multi-level power conversion device (1, 1A, 1B) according to an aspect of embodiments includes a multi-winding transformer (10) and a power conversion unit (20). The multi-winding transformer (10) has a relationship that n secondary windings (12a to 12f) respectively connected to n single-phase power converters (21a to 21f) in the same output phase have a voltage phase difference of 60/n degrees and a relationship that the m secondary windings (12a to 12f) respectively connected to the m single-phase power converters (21a to 21f) corresponding to the m output phases have a voltage phase difference of 60/m degrees.