A pixel calculating device that performs vertical filtering on pixel data in order to reduce frame data in a vertical direction. The pixel calculating device includes a decoding unit 401 for decoding compressed video data to produce frame data, frame memory 402 for storing the frame data, a filtering unit 403 for reducing the frame data in a vertical direction by the vertical filtering to produce a reduced image, buffer memory 404 for storing the reduced image outputted from filtering unit 403, and a control unit 406 for controlling filtering unit 403 based on a decoding state of the video data by decoding unit 401 and a filtering state of the frame data by filtering unit 403, so that overrun and underrun do not occur in filtering unit 403.