Multicore electric wires 31 for connecting an operation key sheet 4a and a control section of an oven body are loosely inserted into a hinge shaft 5b in a cylindrical shape and a door pipe 30 in a cylindrical shape having a length exceeding a half of the height of a door 2, and the door pipe 30 guides the electric wires 31 along the axial direction of the hinge shaft 5b. When the door 2 is opened/closed, torsional stress caused in the electric wires 31 are dispersed over the electric wires 31 disposed correspondingly to the length of the door pipe 30.