Abstract: The invention provides a lift apparatus for use with a ladder having two spaced upright stringers and a plurality of horizontal rungs bridging the stringers and spaced at a distance vertically from one another. The lift apparatus comprises a frame, a prime mover mounted on the frame and having a rotatable output shaft, at least one pair of sprocket systems space apart vertically from each other. At least one of the sprocket systems is operatively coupled with the output shaft of the prime mover. Endless driving force transmitting mechanism can pass around the pair of the sprocket systems. Controller is provided for controlling the prime mover in such a manner as to selectively rotate the output shaft thereof in forward or reverse direction, or stop it. Operating mechanism is provided for causing a plurality of gripper elements to be engaged with the corresponding rungs of the ladder.