A robot according to this invention includes a driving mechanism, a first arm rotatably connected to the driving mechanism, a second arm rotatably connected to the first arm, and an X-shaped end effector rotatably disposed at the distal end of the second arm. Of the four distal ends of the end effector, two distal ends include holding units which can hold substrates in one direction, and the remaining two distal ends include holding units which can hold substrates in the opposite direction.