A median filter device is provided with a reordered circuit, a comparison circuit and a data refresh circuit on the basis of the conventional data buffer circuit and data register circuit. The reorder circuit re-sorts the signal data stored in the data buffer circuit in a preceding clock cycle according to their numerical values. The comparison circuit compares the new signal datum entered in the current clock cycle with the signal data already stored to generate a median. The data refresh circuit updates the signal codes stored in the data register circuit with the signal codes corresponding to the new signal data, for calculation of the median in a following clock cycle. The length of the data buffer circuit and data register circuit can be reduced from N signal data to N−1 signal data, which achieves less data storage capacity, smaller circuit area, easier data processing and higher operation efficiency.