A slide door apparatus for a vehicle includes a driving device mounted to a slide door and a guide pulley unit mounted to the slide door. The guide pulley unit includes a plurality of guide pulleys each having first and second guide grooves. The guide pulley unit further includes first and second housing members for housing the plurality of guide pulleys, and a separating member provided between the first and second housing members for separating the first and second guide grooves of each of the plurality of guide pulleys. The slide door apparatus further includes a cable connected to the driving device and to a vehicle body. A first portion of the cable is disposed into the first groove of each of the plurality of guide pulleys. A second portion of the cable is disposed into the second groove of each of the plurality of guide pulleys.