A leg rest device may a first link member rotatably installed in a front of a seat frame, a second link member installed on a leg plate for supporting legs of a passenger and connected to the first link member to be movable along a longitudinal direction of the first link member, a guide member, one end of which is installed in the seat frame to be rotatable together with the first link member and the other end of which is connected to the second link member to be movable along a longitudinal direction of the second link member, and a driving portion installed in the seat frame. The driving portion, when operating, provides power for the first link member to be rotated, and allows the second link member to be rotated and simultaneously to be moved in the longitudinal direction of the first link member as the guide member is rotated together with the first link member.