A safety device for a hydraulic elevator includes an open-door running prevention unit and a pressure sensor. The open-door running prevention unit includes a memory configured to sequentially store values of the pressure sensor during a period in which the hydraulic elevator is in the open-door state as time-series data. When it is determined that the car speed, detected when the hydraulic elevator is in the open-door state, is equal to or larger than a preset first threshold value, the open-door running prevention unit calculates a differential value between a maximum value and a minimum value of the time-series data stored in the memory in a period of a preset determination time. When the differential value is out of a preset allowable range, the open-door running prevention unit determines that the open-door running abnormality is present, and executes the car braking processing.