A screen film applicator includes a seat, a positioning member, and a first mechanism, the latter two of which are disposed on the seat. The seat has a track and a positioning portion arranged beside the track. The positioning member is movable with respect to the positioning portion for clamping a communication device. The first mechanism includes a top fixing member disposed on the seat, a moving carriage movable along the track, a bottom fixing member synchronously movable with the moving carriage, and a roller movable with the moving carriage. The top and the bottom fixing members are configured to respectively fix a top releasing film and a bottom releasing film respectively adhered on two opposite sides of a soft screen film. When the moving carriage is moved away from the top fixing member, the roller can gradually press the soft screen film onto the communication device.