A cooling device for a forklift brake system, the cooling device comprising: an oil tank in which cooling oil is stored; a hydraulic pump which sucks and discharges the cooling oil; a cooler which cools the discharged cooling oil; a service brake which is cooled by the cooled cooling oil and allows the used cooling oil to be returned to the oil tank; a first bypass line which connects a front end of the service brake and a rear end of the service brake; and a check valve which is installed on the first bypass line, and is opened when an abnormal pressure is generated at the front end of the service brake and allows the cooled cooling oil to bypass the service brake, characterized in that the cooling device further comprising: a second bypass line which is connected from a front end of the cooler 13 to the oil tank; a relief valve which is installed on the second bypass line and is set with a pressure allowable by the cooler, and when the pressure is increased at the front end of the cooler, the relief valve is open to decrease the pressure of the cooling oil; a third bypass line which connects a front end of the cooler and a rear end of the cooler to move the cooling oil which bypassed the cooler to the service brake; and a thermostat valve which is installed on the third bypass line, and is maintained in a closed state when a temperature of the cooling oil discharged from the hydraulic pump is higher than a setting temperature and is opened when the temperature of the cooling oil discharged from the hydraulic pump is lower than the setting temperature to allow the cooling oil to bypass the cooler. an oil tank in which cooling oil is stored; a hydraulic pump which sucks and discharges the cooling oil; a cooler which cools the discharged cooling oil; a service brake which is cooled by the cooled cooling oil and allows the used cooling oil to be returned to the oil tank; a first bypass line which connects a front end of the service brake and a rear end of the service brake; and a check valve which is installed on the first bypass line, and is opened when an abnormal pressure is generated at the front end of the service brake and allows the cooled cooling oil to bypass the service brake, characterized in that the cooling device further comprising: a second bypass line which is connected from a front end of the cooler 13 to the oil tank; a relief valve which is installed on the second bypass line and is set with a pressure allowable by the cooler, and when the pressure is increased at the front end of the cooler, the relief valve is open to decrease the pressure of the cooling oil; a third bypass line which connects a front end of the cooler and a rear end of the cooler to move the cooling oil which bypassed the cooler to the service brake; and a thermostat valve which is installed on the third bypass line, and is maintained in a closed state when a temperature of the cooling oil discharged from the hydraulic pump is higher than a setting temperature and is opened when the temperature of the cooling oil discharged from the hydraulic pump is lower than the setting temperature to allow the cooling oil to bypass the cooler. a second bypass line which is connected from a front end of the cooler 13 to the oil tank; a relief valve which is installed on the second bypass line and is set with a pressure allowable by the cooler, and when the pressure is increased at the front end of the cooler, the relief valve is open to decrease the pressure of the cooling oil; a third bypass line which connects a front end of the cooler and a rear end of the cooler to move the cooling oil which bypassed the cooler to the service brake; and a thermostat valve which is installed on the third bypass line, and is maintained in a closed state when a temperature of the cooling oil discharged from the hydraulic pump is higher than a setting temperature and is opened when the temperature of the cooling oil discharged from the hydraulic pump is lower than the setting temperature to allow the cooling oil to bypass the cooler.