The utility model discloses a seam beautifying device for a building. The device is used for beautifying cement gaps of building walls. The device comprises a main body and a seam beautifying unit which is detachably installed on the main body and used for cleaning and beautifying cement in seams. Idler wheels are arranged on the two sides of the main body, a handle used for being held by hand tobe pushed in a reciprocating mode is arranged at one end of the main body, and the seam beautifying unit comprises a scraper used for scraping cement in a seam and a beautifying wheel used for beautifying and compacting the cement in the seam. According to the device, cement gaps are beautified at a time through the scraper and the beautification wheel, the treatment standards are consistent, anduneven beautification quality is avoided; multi-specification replacement of the seam beautifying unit is conducted through the detachable bottom plate, so that the applicability of the device is wider; the treatment depth of the scraping shovel and the beautifying wheel can be adjusted through the adjusting rod so as to meet the beautifying requirements of different depths; and different patternscan be presented on the cement surface in the gap through the pattern bulges, so that the beautifying effect is greatly improved.