A control device for an internal combustion engine equipped with a supercharger, comprising: intake air amount detection means for detecting an intake air amount; accelerator opening detection means for detecting an accelerator opening degree; engine rotation speed detection means for detecting an engine rotation speed; ambient pressure read means for reading an ambient pressure; overlap read means for reading a valve overlap period; collector pressure detection means for detecting a collector pressure; exhaust gas pressure estimation means for estimating an exhaust gas pressure on an upstream side of the supercharger; and scavenging amount estimation means for estimating a scavenging amount based on the engine rotation speed, the valve overlap period, the collector pressure, and the exhaust gas pressure, wherein the exhaust gas pressure estimation means comprises: a steady exhaust gas pressure estimation module for estimating an exhaust gas pressure in a steady operation state based on at least an exhaust gas temperature, the intake air amount and the ambient pressure; and a transient-exhaust-gas-pressure-variation amount estimation module for estimating an exhaust-gas-pressure-change amount in a transient operation state based on at least the intake air amount and the accelerator opening degree, wherein the exhaust gas pressure estimation means estimates the exhaust gas pressure by correcting an estimated value of the exhaust gas pressure in the steady operation state by an estimated value of the exhaust-gas-pressure-change amount in the transient operation state, and wherein the transient-exhaust-gas-pressure-variation amount estimation module estimates the exhaust-gas-pressure-change amount in the transient operation state by considering a pressure loss of the supercharger based on a change speed of an intake air amount or a change speed of a throttle valve opening area. intake air amount detection means for detecting an intake air amount; accelerator opening detection means for detecting an accelerator opening degree; engine rotation speed detection means for detecting an engine rotation speed; ambient pressure read means for reading an ambient pressure; overlap read means for reading a valve overlap period; collector pressure detection means for detecting a collector pressure; exhaust gas pressure estimation means for estimating an exhaust gas pressure on an upstream side of the supercharger; and scavenging amount estimation means for estimating a scavenging amount based on the engine rotation speed, the valve overlap period, the collector pressure, and the exhaust gas pressure, wherein the exhaust gas pressure estimation means comprises: a steady exhaust gas pressure estimation module for estimating an exhaust gas pressure in a steady operation state based on at least an exhaust gas temperature, the intake air amount and the ambient pressure; and a transient-exhaust-gas-pressure-variation amount estimation module for estimating an exhaust-gas-pressure-change amount in a transient operation state based on at least the intake air amount and the accelerator opening degree, a steady exhaust gas pressure estimation module for estimating an exhaust gas pressure in a steady operation state based on at least an exhaust gas temperature, the intake air amount and the ambient pressure; and a transient-exhaust-gas-pressure-variation amount estimation module for estimating an exhaust-gas-pressure-change amount in a transient operation state based on at least the intake air amount and the accelerator opening degree, wherein the exhaust gas pressure estimation means estimates the exhaust gas pressure by correcting an estimated value of the exhaust gas pressure in the steady operation state by an estimated value of the exhaust-gas-pressure-change amount in the transient operation state, and wherein the transient-exhaust-gas-pressure-variation amount estimation module estimates the exhaust-gas-pressure-change amount in the transient operation state by considering a pressure loss of the supercharger based on a change speed of an intake air amount or a change speed of a throttle valve opening area.