PURPOSE: To improve the sensitivity, preservation stability, etc., and to reduce the red light sensitivity, fogging, etc. by sensitizing chemically a silver halide photographic emulsion with a water-soluble metallic compd., an unstable sulfur compd., and a specified selenium compd.

CONSTITUTION: (A) 1×10-9W1×10-4mol water-soluble gold compd. (e.g., chloroauric acid) based on 1mol silver halide, (B) 1×10-7W1×10-3mol unstable sulfur compd. (e.g., ammonium thiosulfate) based on 1mol silver halide, and (C) a compd. (e.g., formulas II and III) expressed by the formula I [Z is a nonmetallic atom group necessary for forming a nitrogen-contg. heterocyclic ring, R1 and R2 are H, alkyl, etc., and (n) is 0, 1, and 2] are added to a silver halide photographic emulsion to sensitize chemically the emulsion. In addition, the compd. of the formula I can be obtained by dissolving a compd. shown by the formula IVin a solvent, heating, adding carbon diselenide, and allowing to react.