To provide a flame retardant imparting a high flame retardancy to a resin while suppressing content of a hydrous metal compound at a reduced amount, and to provide a flame retardant resin composition compounded with the flame retardant.

The flame retardant comprises the hydrous metal compound, a nitrate and phosphorus or a phosphorus compound as the component imparting the flame retardancy to the resin. The degradation of the resin compounded with the flame retardant is promoted at a temperature region lower than the starting temperature of burning.