A filter cleaning device has an improved structure which is capable of effectively cleaning dust in a filter used in an air conditioner. The filter cleaning device includes: a filter; a brush unit movably installed at one side of the filter to separate dust from the filter; a brush movement unit configured so that the brush unit is movable along the filter; and brush guides installed at two sides of the brush unit to guide a movement of the brush unit. Each of the brush guides includes: a first guide groove formed so that the brush unit is moved to be in contact with the filter; and a second guide groove formed so that the brush unit is moved to be separated from the filter.