A linear motion device includes: a linear motion mechanism having: a beam elongated in one horizontal direction; a guide member disposed in the beam to extend in the one direction; a moving member disposed to be movable along the guide member; and a moving mechanism that moves the moving member. The beam includes a metallic tubular body formed with an opening portion penetrating the metallic tubular body in the one direction and a tubular reinforcing portion formed of a carbon fiber reinforced plastic and formed in close contact with an inner surface of the metallic tubular body.