Disclosed is a handle structure of an apparatus for opening and closing a window capable of allowing a user to open and close the window with safety. The handle structure may be mounted to a driving shaft installed in a housing of the apparatus for opening and closing the window and may then be foldable. In the handle structure, a depressed portion is formed on an inner surface of a body portion of the handle structure and extends along the longitudinal direction. Pair of fixed members is formed on the inner surface of the body portion within the depressed portion and extend over a predetermined length of the depressed portion. A supporting device is suitably secured together with the fixed members formed in the depressed portion. The supporting device is provided with a rectangular plate-shaped supporting piece, a hexahedral-shaped moving member and a coiled spring. A knob is engaged to be one body with an outer surface of one end portion of the body portion. A bore is formed at an inner side of the other end portion of the body portion. A joining member having an inserting portion and a locking portion is mounted in the bore. The body portion may be pivoted with centering on a joining pin for fixing the joining member to the body portion. When the handle structure is not to be use, it can be folded. This handle structure can be maintained with safety whether it is to be use or not.