To provide a hydraulic locking device, capable of enhancing sureness and reliability in operating a device, intending for miniaturization and a high output of the device, and for attaining miniaturization and a low pressure of a hydraulic supply source.

A hydraulic cylinder 4 to cause a rod 3 to move axially is provided, a ring booster 7 to pressurize oil in a hydraulic chamber 6 on its peripheral side is provided in a case member 2, a hydraulic supply port for supplying oil pressure to the hydraulic cylinder 4 and the input oil chamber 16 of the booster 7 is provided in the case member 2, a throttle valve is interposed in a supply oil passage leading to the input oil chamber 16 from the hydraulic supply port, and a check valve 9 capable of discharging the oil pressure of the input oil chamber 16 to an discharge oil passage leading to the hydraulic supply port from the input oil chamber 16, whir opening, when discharging the oil pressure from the hydraulic supply port is provided.