For finite Volterra series systems, this paper investigates the stability of the exact model matching (EMM) control we have already presented. First, in order to analyze the stability of the EMM system, we present modified small gain theorems depending on the magnitude of the external input (s) in the cases of one input and two inputs. Next, with the help of the theorem for feedback systems with two inputs, we clarify the condition under which the control system is stable for the reference input magnitude within a certain range, and is also robust for small disturbances. The modified small gain theorems are effective for the stability analysis of the nonlinear feedback control systems which do not have affine finite gain.