PURPOSE: To easily remove a low melting metal core without receiving any restriction in the position and shape of the low melting metal core in a cast product by immersing the cast product contg. the low melting metal core into a salt bath in which nitrates are melted by heating, thereby dissolving away the low melting metal core.

CONSTITUTION: The liquid salt bath 3 is prepd. by putting a mixture composed of sodium nitrate and potassium nitrate into a dissolving away vessel B and melting the mixture by heating. The temp. of the salt bath 3 of the nitrates is set higher by plus 50°C than the m.p. of the low melting metal core 1 to be eluted. The cast product A contg. the low melting metal core 1 is directly heated by the salt bath 3 of the nitrates and simultaneously the low melting metal core 1 in the cast product A is heated by coming partly into direct contact with the nitrates 3 when the cast product A is immersed into the nitrates 3. Consequently, the low melting metal core 1 in the cast product A is rapidly dissolved and is eluted from the core taking-out part 2 of the cast product A into the dissolving away vessel B and is thus removed from the cast product A.