To obtain a simultaneously biaxially stretched polyamide film low in the anisotropicity of thrinkage characteristics of the film in all of directions excellent in thermal dimensional stability and having practical strength.

In a process for producing a simultaneously biaxially stretched polyamide film by transferring a substantially amorphous and unoriented unstretched film to a temp. conditioned water tank to apply water absorbing treatment thereto and stretching this film in longitudinal (MD) and lateral (TD) directions by a tenter type simultaneous biaxial stretching machine, both ends of this stretched film are released from the clips of the tenter type simultaneous biaxial stretching machine after the completion of stretching, heat treatment and slackening treatment to be reheated under a condition satisfying formula I: MD1>MD2, formula II: reheating treatment temp. is 160-22°C and formula III: 0<T≤0.5 [wherein MDI is the hot water shrinkage factor in the MD direction of the film before reheating treatment, MD2 is the hot water shrinkage factor in the MD direction of the film after reheating treatment and T is the tension (tension kgf per the thickness of 1 μm and the film width of 1 m) in the running direction of the film at a time of reheating treatment] by a floating type heat treatment apparatus.