A three-way valve comprising: a valve housing in which an inlet through which heating water is introduced, a first outlet configured to supply the heating water introduced through the inlet to a heating target area, and a second outlet configured to supply the heating water introduced through the inlet to a hot water heat exchanger are integrally formed; a first valve member configured to be opened or closed so as to selectively open any one of the first outlet and the second outlet; a drive unit configured to provide a driving force to open or close the first valve member; and a second valve member (220, 220-1) configured to, when a pressure of heating water of a side of the first outlet is higher than a set pressure in a state in which the first valve member opens a side of the first outlet and closes a side of the second outlet, open a bypass hole to allow the heating water to flow toward the second outlet and be operated independently from the first valve member, characterized in that the first valve member is coupled to a valve shaft linearly moved by the drive unit; the first valve member includes a heating side valve coupled to one side of the valve shaft and configured to open or close a first opening which communicates with the first outlet, and a hot water side valve coupled to the other side of the valve shaft and configured to open or close a second opening which communicates with the second outlet; and the valve shaft and the first valve member is pushed toward the drive unit by an elastic force of a first spring, a valve seat member, configured to seal a space between the first valve member and the second valve member (220, 220-1), is inserted into the valve housing; and the valve seat member is formed by integrally forming a first valve seat portion through which the first opening is formed in the valve seat member, a second valve seat portion through which the second opening is formed in the valve seat member, and a plurality of connecting portions connecting the first valve seat portion and the second valve seat portion. a valve housing in which an inlet through which heating water is introduced, a first outlet configured to supply the heating water introduced through the inlet to a heating target area, and a second outlet configured to supply the heating water introduced through the inlet to a hot water heat exchanger are integrally formed; a first valve member configured to be opened or closed so as to selectively open any one of the first outlet and the second outlet; a drive unit configured to provide a driving force to open or close the first valve member; and a second valve member (220, 220-1) configured to, when a pressure of heating water of a side of the first outlet is higher than a set pressure in a state in which the first valve member opens a side of the first outlet and closes a side of the second outlet, open a bypass hole to allow the heating water to flow toward the second outlet and be operated independently from the first valve member, characterized in that the first valve member is coupled to a valve shaft linearly moved by the drive unit; the first valve member includes a heating side valve coupled to one side of the valve shaft and configured to open or close a first opening which communicates with the first outlet, and a hot water side valve coupled to the other side of the valve shaft and configured to open or close a second opening which communicates with the second outlet; and the valve shaft and the first valve member is pushed toward the drive unit by an elastic force of a first spring, a valve seat member, configured to seal a space between the first valve member and the second valve member (220, 220-1), is inserted into the valve housing; and the valve seat member is formed by integrally forming a first valve seat portion through which the first opening is formed in the valve seat member, a second valve seat portion through which the second opening is formed in the valve seat member, and a plurality of connecting portions connecting the first valve seat portion and the second valve seat portion.