A sliding door device for a vehicle includes a sliding door installed to be slidingly moved, a door weather strip attached to the sliding door, a pressure switch for sensing internal pressure of the door weather strip, a pneumatic line for connecting the door weather strip and the pressure switch to communicate with each other, an electronic control unit (ECU) for receiving a sensing signal of the pressure switch to control opening and closing of the sliding door, and an opening and closing valve for having the pneumatic line communicate with the atmospheric pressure or blocking the pneumatic line from the atmospheric pressure. Therefore, it is possible to effectively prevent an object or an occupant from being jammed in a process of closing the sliding door.