  Using the variational method, Chenciner and Montgomery (2000 Ann. Math. 152
881--901) proved the existence of an eight-shaped periodic solution of the
planar three-body problem with equal masses. Just after the discovery, Gerver
have numerically found a similar periodic solution called "super-eight" in the
planar four-body problem with equal mass.
  In this paper we prove the existence of the super-eight orbit by using the
variational method. The difficulty of the proof is to eliminate the possibility
of collisions. In order to solve it, we apply the technique established by
Tanaka (1993 Ann. Inst. H. Poincar'e Anal. Non Lin'eaire 10, 215--238, 1994
Proc. Amer. Math. Soc. 122, 275--284).
