An engine brake apparatus may include an exhaust rocker arm having a chamber in which an actuator is slidably inserted, an oil line coupling part which has a central portion extrapolated with an oil line, a communication line communicating with the oil line, a distribution line branched from the communication line and having one portion extending toward a check ball and another portion extending toward a relief valve, a supply line including one portion connected to the check ball and another portion connected to the chamber, and a discharge line including one portion connected to the relief valve and another portion connected to the chamber, wherein the check ball is elastically supported by a check spring in a direction in which the distribution line is closed, and wherein the relief valve is elastically supported by a relief spring in a direction in which the discharge line is opened.