  The full analytical solution of the Schr\"{o}dinger equation for the hydrogen
molecular ion $H_2^+$ (special case of the quantum tree-body problem with the
Coulomb interaction) is obtained first. The solution shows that the total wave
function is a two-term function in the sense that it is a linear combination of
the two linear independent wave functions. The two-term character of the total
wave function was visualized in calculations of the total electron density of
$H_2^+$ at different internuclear separations.
