The rectifier includes: a main circuit unit configured to perform power conversion between AC power on a side of a three-phase AC power supply and DC power on a DC side by rectifying operation of a rectifying device and ON-OFF operation of a switching device; a power calculation unit configured to calculate a value of a power flowing between the side of the three-phase AC power supply and the DC side via the main circuit unit; and a control unit configured to perform control to execute the ON-OFF operation of the switching device, wherein the control unit changes a length of an ON period per cycle in the ON-OFF operation executed on the switching device according to the value of the power calculated by the power calculation unit.