PURPOSE: To prepare fine powder of a metal compd. having very small and uniform particle size and high purity with high synthesizing yield by ejecting a gaseous mixture consisting of a metal and carrier gas into the partner element or a gas contg. the partner element with a specified velocity.

CONSTITUTION: A gaseous mixture consisting of a metal (e.g. Si) constituting a metal compd. (e.g. silicon nitride) and carrier gas (e.g. N2) for the metal is prepd. in a mixing chamber 8, and the gaseous mixture is ejected into a partner element constituting the metal compd. or into a gaseous atmosphere of a gas (e.g. NH3) contg. said partner element contained in a bottom chamber 4 at a temp. ≤80% of the m.p. of the metal with 50W2,000m/sec velocity through a small dia. pipe 11. By this method, the metal is allowed to react with the partner element by cooling rapidly. As the result, fine powders of the metal compd. having very small and substantially uniform particle size and high purity are prepd.