A key apparatus of an electronic device is provided. The key apparatus includes a housing having a cylindrical portion, the cylindrical portion including an upper portion and a lower portion, the upper portion and the lower portion being open, a knob including a circular-plate portion, the circular plate portion having a concavo-convex portion, the concavo-convex portion including a concave portion and a convex portion arranged alternately in a circular shape and an extension portion extended from the circular-plate portion in a downward direction and inserted into a hollow of the cylindrical portion, and the knob moves on the circular-plate portion, an anti-deviation unit configured to prevent the knob from being deviated from the cylindrical portion, an elastic configured to elastically press the concavo-convex portion at a lower side of the circular-plate portion, and a switch connected to the extension portion and switches over movement of the extension portion is delivered.