  A Bose-Einstein condensate with attractive interaction can be metastable if
it is spatially confined and if the number of condensate bosons $N_0$ is below
a certain critical value $N_{\rm c}$. By applying a variational method and the
instanton techinique to the Gross-Pitaevskii energy functional, we find
analytically the frequency of the collective excitation and the rate of
macroscopic quantum tunneling (MQT). We show that near the critical point the
tunneling exponent vanishes according to $(1-N_0/N_c)^\frac{5}{4}$ and that MQT
can be a dominant decay mechanism of the condensate for $N_0$ very close to
$N_{\rm c}$.
