Disclosed is an easy-to-construct window apparatus including to assure easy construction and superior drainage ability. The window apparatus includes a window frame fixing unit including a bottom plate, vertical plates formed at lateral ends of the bottom plate and a rack plate formed at each vertical plate, a window frame support unit including a seat plate on the rack plate, a support plate configured to be supported on the bottom plate, fastening pieces protruding from the seat plate, and a holding groove formed in each fastening piece, a rail unit including a horizontal plate provided with a rail and a coupling piece, and a holding ridge formed at the coupling piece so as to be coupled with the holding groove, a window drive unit including a press-fit structure to be press-fitted into a window, and water discharge holes perforated in the aforementioned units.