An antireflection film composition, wherein an etching speed is fast, thus, when used as a resist lower layer, a film loss of a resist pattern and deformation of the pattern during etching can be minimized, and because of a high crosslinking density, a dense film can be formed after thermal crosslinking, thus, mixing with an upper layer resist can be prevented and the resist pattern after development is good is provided. The antireflection film composition comprising; at least a polymer having a repeating unit represented by the following general formula (I).