The present invention relates to a novel compound which is useful as an agent for prevention and treatment of diseases associated with HDAC, in particular, tumor or cell proliferative diseases. The depsipeptide compound or its pharmaceutically acceptable salt of the present invention has a good HDAC inhibitory activity and an inhibitory activity of cell proliferation against human cancer cells and, therefore, is useful in treatment and improvement of diseases and pathogenic conditions associated with histone acetylation, in particular, tumor or cell proliferative diseases.