A variable compression ratio internal combustion engine comprising: a compression ratio changing mechanism that can change the compression ratio of the internal combustion engine; a supercharger driven by exhaust gas from said internal combustion engine for supercharging intake air to said internal combustion engine; and basic compression ratio derivation means for deriving a basic compression ratio with which a specific heat efficiency can be achieved with knocking in said internal combustion engine being suppressed, in accordance with a running condition of said internal combustion engine, wherein while said internal combustion engine is running, the compression ratio of the internal combustion engine is set to said basic compression ratio by said compression ratio changing mechanism, characterized in that when said internal combustion engine enters a specific acceleration state, in which the required acceleration is higher than or equal to a threshold acceleration above which the influence of the response delay of the supercharger becomes noticeable when the compression ratio is set to the aforementioned basic compression ratio, the compression ratio of the internal combustion engine is changed by said compression ratio changing mechanism to a specific compression ratio suitable for acceleration that is lower than said basic compression ratio, and that the compression ratio of the internal combustion engine is set by said compression ratio changing mechanism to said compression ratio suitable for acceleration during a period after acceleration of said internal combustion engine has been started until supercharging pressure of said supercharger becomes larger than or equal to a specific pressure. a compression ratio changing mechanism that can change the compression ratio of the internal combustion engine; a supercharger driven by exhaust gas from said internal combustion engine for supercharging intake air to said internal combustion engine; and basic compression ratio derivation means for deriving a basic compression ratio with which a specific heat efficiency can be achieved with knocking in said internal combustion engine being suppressed, in accordance with a running condition of said internal combustion engine, wherein while said internal combustion engine is running, the compression ratio of the internal combustion engine is set to said basic compression ratio by said compression ratio changing mechanism, characterized in that when said internal combustion engine enters a specific acceleration state, in which the required acceleration is higher than or equal to a threshold acceleration above which the influence of the response delay of the supercharger becomes noticeable when the compression ratio is set to the aforementioned basic compression ratio, the compression ratio of the internal combustion engine is changed by said compression ratio changing mechanism to a specific compression ratio suitable for acceleration that is lower than said basic compression ratio, and that the compression ratio of the internal combustion engine is set by said compression ratio changing mechanism to said compression ratio suitable for acceleration during a period after acceleration of said internal combustion engine has been started until supercharging pressure of said supercharger becomes larger than or equal to a specific pressure.