To provide a hydraulic system which can inexpensively and quickly detect the temperature of oil without using a temperature sensor, and can quickly perform the temperature rise control.

A temperature rise control means 25 compares the electric current detected by an electric current detecting means 26 with the reference electric current stored beforehand in the idling state at a start or in the pressure holding state of a hydraulic cylinder 5. When the detected electric current is larger than the reference electric current, the temperature-rise control means 25 closes the portion between a pump port P and a first load port A by positioning an electromagnetic selector valve 2 to a neutral position S0, and also controls a hydraulic pump 1 via a motor 15 so as to open a relief valve 11. Thus, the temperature-rise control can be inexpensively and quickly performed by estimating the temperature of oil by the electric current without using a temperature sensor.