An image decoding device comprising: circuitry configured to receive an encoded image block to be decoded, a filter block flag for controlling whether or not a filtering process is performed on an image block, a boundary control flag for controlling whether the filtering process, performed on a target pixel which is adjacent to a slice boundary separating a slice including said target pixel and a neighboring slice of said slice and which is provided within the image block of the slice, uses pixels of said neighboring slice after the pixels of said neighboring slice are available or whether the filtering process, performed on the target pixel, uses pixels of the slice alone, the pixels to be used are surrounding pixels surrounding said target pixel, and block size information of the encoded image block; obtain a position of the encoded image block based on the block size information; decode the encoded image block; and perform the filtering process on the decoded image block based on the filter block flag, the boundary control flag, and the position of the encoded image block, wherein, in the event that the boundary control flag indicates to use pixels of the slice alone, said filter processing as to said target pixel to be processed is performed assuming a dummy value for each of the surrounding pixels that are in said neighboring slice, whereby the assumed dummy value is based on pixels of the slice alone. circuitry configured to receive an encoded image block to be decoded, a filter block flag for controlling whether or not a filtering process is performed on an image block, a boundary control flag for controlling whether the filtering process, performed on a target pixel which is adjacent to a slice boundary separating a slice including said target pixel and a neighboring slice of said slice and which is provided within the image block of the slice, uses pixels of said neighboring slice after the pixels of said neighboring slice are available or whether the filtering process, performed on the target pixel, uses pixels of the slice alone, the pixels to be used are surrounding pixels surrounding said target pixel, and block size information of the encoded image block; an encoded image block to be decoded, a filter block flag for controlling whether or not a filtering process is performed on an image block, a boundary control flag for controlling whether the filtering process, performed on a target pixel which is adjacent to a slice boundary separating a slice including said target pixel and a neighboring slice of said slice and which is provided within the image block of the slice, uses pixels of said neighboring slice after the pixels of said neighboring slice are available or whether the filtering process, performed on the target pixel, uses pixels of the slice alone, the pixels to be used are surrounding pixels surrounding said target pixel, and block size information of the encoded image block; obtain a position of the encoded image block based on the block size information; decode the encoded image block; and perform the filtering process on the decoded image block based on the filter block flag, the boundary control flag, and the position of the encoded image block, wherein, in the event that the boundary control flag indicates to use pixels of the slice alone, said filter processing as to said target pixel to be processed is performed assuming a dummy value for each of the surrounding pixels that are in said neighboring slice, whereby the assumed dummy value is based on pixels of the slice alone.