A method of controlling a window cleaning apparatus according to an embodiment of the present invention, which are attached to inner and outer sides of a window by magnetic force, is capable of maintaining constantly magnetic force by initializing magnetic force between first and second cleaning units. Also, cleaning units according to another embodiment of the present invention, which are attached to inner and outer side of a window by magnetic force, may increase a user's convenience by automatically setting first and second cleaning units for an available cleaning pair among multiple pairs of first and second cleaning units during an initial operation.