A device for eliminating a block artifact phenomenon of a decoded image frame, and an eliminating method thereof. A method for eliminating a block artifact phenomenon according to the present invention includes: extracting pixel information including a magnitude of edge response, an edge direction, and an edge position, by applying an edge detector to an arbitrary pixel in an image frame; distinguishing the pixel into a non-edge pixel, an object edge pixel, or a block edge pixel by using the extracted pixel information; and performing filtering according to the distinguishing result. In this manner, an object edge information is selectively protected, so that an improved image quality may be provided.