  The progress in investigation of two-band superconductor MgB$_2$ by the
point-contact spectroscopy (PCS) is given. Results of study of superconducting
gap temperature and magnetic field dependence for two-dimensional $\sigma$ and
three-dimensional $\pi$ band and electron-phonon-interaction spectral function
are presented. Correlation between the gap value and the intensity of the high
T$_c$ driving force -- $E_{2g}$ boron vibration mode, is provided. PCS data on
some nonsuperconducting transition metal diborides are surveyed for comparison.
