A sliding door device for a vehicle includes a door arm including a first end portion rotatably connected to an end portion of the door and a second end portion movable along a side sill of the vehicle body, a door power connection portion provided in the door arm, and a vehicle power connection portion provided in a position corresponding to the door power connection portion of the vehicle body and electrically connected to the door power connection portion according to rotation of the door arm, wherein the vehicle power connection portion includes: a first vehicle power connection portion electrically connected to the door power connection portion when the door is closed, and a second vehicle power connection portion electrically connected to the door power connection portion when the door is opened.