The present invention relates to novel compounds having a histone deacetylase 6 (HDAC6) inhibitory activity, optical isomers thereof or pharmaceutically acceptable salts thereof, a pharmaceutical use thereof, and a method for preparing the same. According to the present invention, the novel compounds, optical isomers thereof or pharmaceutically acceptable salts thereof have the histone deacetylase 6 (HDAC6) inhibitory activity, and are effective in preventing or treating HDAC6-related diseases, comprising infectious diseases; neoplasm; internal secretion; nutritional and metabolic diseases; mental and behavioral disorders; neurological diseases; eye and ocular adnexal diseases; circulatory diseases; respiratory diseases; digestive diseases; skin and subcutaneous tissue diseases; musculoskeletal system and connective tissue diseases; and teratosis or deformities, and chromosomal aberration.