A method for maintaining a floating wind-power generation device wherein a wind-power generator is installed on top of a floating body moored at a mooring position by a mooring line and electric power generated by said wind-power generator is supplied to a cable. Said method comprises the following steps: a separation step in which the aforementioned mooring line and cable are separated from the floating body of a first floating wind-power generation device that has a site where maintenance is to be performed; a holding step in which, after the separation step, a floating structure is made to hold the aforementioned mooring line and cable; a first movement step in which, after the separation step, the first floating wind-power generation device is moved from the abovementioned mooring position; a second movement step in which a second floating wind-power generation device that does not have a site where maintenance is to be performed is moved to the abovementioned mooring position; and a connection step in which, after the second movement step, the abovementioned mooring line and cable are detached from the abovementioned floating structure and connected to the second floating wind-power generation device.