The invention relates to an encoder. The encoder comprises a rotating shaft, a flexible connection member, a housing, soft cotton and an inner shell, wherein the inner shell is arranged in the housing; the soft cotton is filled in the space between the housing and the inner shell; the rotating shaft is arranged at the central axis position of the inner shell; one end of the rotating shaft stretches out from the housing along the central axis; and the end portion, stretching out from the housing, of the rotating shaft, is provided with the flexible connection member. The encoder is used for measuring the rotating speed of a roller in the steel industry, wherein the soft cotton between the inner shell and the housing and the flexible connection member at the end portion of the rotating shaft can reduce the mechanical oscillation amplitude that the encoder bears so as to protect the internal precise parts in the encoder. Therefore, the encoder can effectively guarantee the measuring accuracy and the service life of the encoder.