A back reclining apparatus interlocking with a seat cushion for a vehicle may include a back frame including a main frame fixed to a vehicle body and a reclining frame that may be selectively reclined around a reclining hinge on an inner surface of the main frame, a reclining locking unit connected to the main frame and the reclining frame to selectively release locking of the main frame and the reclining frame, a cushion locking unit selectively releasing locking of a cushion frame and the reclining frame, and a cushion sliding unit connected between the cushion frame and a floor panel to interlock with the reclining frame and to make the cushion frame move to slide forward when the locking of the reclining locking unit may be released and the reclining frame may be reclined around the reclining hinge.