An engine system utilizing a hydraulic pressure includes an engine, a hydraulic system having at least one hydraulic pump discharging a hydraulic oil for operating an actuator and a hydraulic oil tank storing the hydraulic oil returned from the actuator, a hydraulic power transmission device connected to a hydraulic line between the hydraulic pump and the hydraulic oil tank and configured to transmit a hydraulic pressure of the hydraulic oil as a driving source, and a vehicular auxiliary device driven by using the hydraulic pressure transmitted from the hydraulic power transmission device as the driving source.