A method of maintaining a power generating apparatus includes a separation step of separating a mooring line and a cable from a floating body of a first floating-body type wind turbine power generating apparatus including a maintenance-target section; a retention step of retaining the mooring line and the cable by a floating-body structure, after the separation step; a first transfer step of transferring the first floating-body type wind turbine power generating apparatus from the mooring position, after the separation step; a second transfer step of transferring a second floating-body type wind turbine power generating apparatus having no maintenance-target section to the mooring position; and a connection step of detaching the mooring line and the cable from the floating-body structure and connecting the mooring line and the cable to the second floating-body type wind turbine power generating apparatus, after the second transfer step.