A filter cleaning device for an air-conditioner, comprising: a flat filter having a filter surface and configured to pass an air flow through the filter surface; a brush unit having a brush and a storage member, the brush being configured to contact with the filter surface, and the storage member being disposed under the brush, configured to receive particles falling from the brush, and forming a bottom surface of the brush unit; a driving unit configured to move the brush unit such that a relative position of the brush relative to the filter moves along a first moving axis which extends substantially horizontally and along the filter surface; a controller configured to control the driving unit such that the relative position of the brush unit moves from one end side to the other end side of the filter with respect to the first moving axis; and a housing accommodating the filter, the brush unit and the driving unit, a first hole being formed within a bottom surface of the housing; wherein the filter is fixed to a position with respect to the housing, and the housing is configured such that the first hole is formed at a first position adjacent to one end side of the filter with respect to the first moving axis, characterized in that: the storage member is of a transparent material; the housing and storage member are formed such that the first hole of the housing is to be closed with the bottom surface of the storage member; and the controller is configured to control the driving unit such that the storage member is located directly over the first hole in non-use state of the filter cleaning device. a flat filter having a filter surface and configured to pass an air flow through the filter surface; a brush unit having a brush and a storage member, the brush being configured to contact with the filter surface, and the storage member being disposed under the brush, configured to receive particles falling from the brush, and forming a bottom surface of the brush unit; the brush being configured to contact with the filter surface, and the storage member being disposed under the brush, configured to receive particles falling from the brush, and forming a bottom surface of the brush unit; a driving unit configured to move the brush unit such that a relative position of the brush relative to the filter moves along a first moving axis which extends substantially horizontally and along the filter surface; a controller configured to control the driving unit such that the relative position of the brush unit moves from one end side to the other end side of the filter with respect to the first moving axis; and a housing accommodating the filter, the brush unit and the driving unit, a first hole being formed within a bottom surface of the housing; wherein the filter is fixed to a position with respect to the housing, and the housing is configured such that the first hole is formed at a first position adjacent to one end side of the filter with respect to the first moving axis, characterized in that: the storage member is of a transparent material; the housing and storage member are formed such that the first hole of the housing is to be closed with the bottom surface of the storage member; and the controller is configured to control the driving unit such that the storage member is located directly over the first hole in non-use state of the filter cleaning device. the storage member is of a transparent material; the housing and storage member are formed such that the first hole of the housing is to be closed with the bottom surface of the storage member; and the controller is configured to control the driving unit such that the storage member is located directly over the first hole in non-use state of the filter cleaning device.