The purpose of the present invention is to provide a polyamide fiber from which a fabric appropriate for use in airbags is obtainable, and which exhibits weave-loosening prevention properties after weaving thereof, and excellent mechanical properties. This polyamide fiber is characterized by having; a total fiber density of 100-700 dtex; a tensile strength of 8.0-11.5 cN/dtex; a boiling-water shrinkage of 4.0-11.0%; a slack recovery rate (A) represented by formula (1) after a fixed-length heat treatment of 0-4.0%; and a tightening index (F) represented by formula (2) of 3.8 or higher. A=[(Ta−Tb)/Ta]×100 (1) (In formula (1), Ta represents the amount of slack immediately after heat treatment, and Tb represents the amount of slack at the time of stabilization after heat treatment.) F=A+0.35×B (2) (In formula (2), A represents the slack recovery rate after the fixed-length heat treatment, and B represents the boiling-water shrinkage rate.)