The Large Helical Device (LHD) is an experimental heliotron-type fusion plasma which consisting of a complete superconducting magnet system cooled by a helium refrigerator having a total equivalent cooling capacity of 9.2 kW@4.4 K. Eighteen plasma experimental campaigns have been performed successfully since 1997, with a high reliability of 99%. Seventeen years have passed since beginning system operation. During the operational history, appropriate improvements have been implemented to prevent serious failures and to pursue further reliability. The operational history of the LHD cryogenic system is reported along with improvements that have been made to the system.