  The mechanism of $p^3$He backward elastic scattering is studied.
  It is found that the triangle diagrams with the subprocesses $pd\to ^3$He$
\pi^0$,
  $pd^*\to ^3$He$ \pi^0$ and $p(pp)\to^3$He$ \pi^+$, where $d^*$ and $pp$
denote the singlet deuteron and diproton pair in the $^1S_0$ state,
respectively, dominate in the cross section at 0.3-0.8 GeV, and their
contribution is comparable with that for a sequential transfer of a $np$ pair
at 1-1.5 GeV.
  The contribution of the $d^*+pp$, estimated on the basis of the spectator
mechanism of the $p(NN)\to ^3$He$ \pi$ reaction, increases the $p^3$He$\to
^3$He$ p$ cross section by one order of magnitude as compared to the
contribution of the deuteron alone.
  Effects of the initial and final states interaction are taken into account.
