An electric oven comprising: a case; a heating chamber in the case; a door that opens and closes the heating chamber, wherein the door includes a first glass facing the heating chamber, a second glass located proximate the first glass, the first and second glasses (210, 220) forming a first air gap in the door, a valve provided in the door, wherein the valve is configured to either permit air to enter the first air gap to cool the door or prevent air from entering the first air gap to insulate heat in the heating chamber, the door comprises a third glass located proximate to the second glass to form a second air gap between the second and third glasses (220, 230), characterized in that the door comprises a supporter which supports the first, second, and third glasses (210, 220, 230) thereon, wherein the supporter is configured to permit air to flow into the second air gap while preventing air from flowing into the first air gap; the oven further comprising a lock that selectively locks the door, wherein the valve is operatively coupled to the lock such that the lock controls movement of the valve, wherein the valve comprises: a first member that opens and closes a portion of the first air gap; a second member movable along with the first member, and the lock is configured to move both the first and second members (261, 263); a pivot about which the first and second members (261, 263) rotate together when the lock touches the second member; and an elastic member which allows the first and second members (261, 263) to return to an initial position of the first and second members (261, 263). a case; a heating chamber in the case; a door that opens and closes the heating chamber, wherein the door includes a first glass facing the heating chamber, a second glass located proximate the first glass, the first and second glasses (210, 220) forming a first air gap in the door, a valve provided in the door, wherein the valve is configured to either permit air to enter the first air gap to cool the door or prevent air from entering the first air gap to insulate heat in the heating chamber, the door comprises a third glass located proximate to the second glass to form a second air gap between the second and third glasses (220, 230), characterized in that the door comprises a supporter which supports the first, second, and third glasses (210, 220, 230) thereon, wherein the supporter is configured to permit air to flow into the second air gap while preventing air from flowing into the first air gap; the oven further comprising a lock that selectively locks the door, wherein the valve is operatively coupled to the lock such that the lock controls movement of the valve, wherein the valve comprises: a first member that opens and closes a portion of the first air gap; a second member movable along with the first member, and the lock is configured to move both the first and second members (261, 263); a pivot about which the first and second members (261, 263) rotate together when the lock touches the second member; and an elastic member which allows the first and second members (261, 263) to return to an initial position of the first and second members (261, 263). a first member that opens and closes a portion of the first air gap; a second member movable along with the first member, and the lock is configured to move both the first and second members (261, 263); a pivot about which the first and second members (261, 263) rotate together when the lock touches the second member; and an elastic member which allows the first and second members (261, 263) to return to an initial position of the first and second members (261, 263).