Disclosed is an exhaust valve capable of correctly opening/shutting an exhaust port of a cylinder based upon variation of the flux density of an electromagnet. The inventive exhaust valve may comprise a guide connected in parallel to an exhaust port of a cylinder, a needle valve provided inside the guide for opening/shutting the exhaust port while moving in cooperation with the guide. The needle valve may be controlled with an electromagnet. The invention enables complete opening of the exhaust port of the cylinder in exhaustion thereby preventing degradation of compression efficiency due to valve damage while reducing generation of vibration and noise.