A control method for an internal combustion engine , the internal combustion engine including: - a variable compression ratio mechanism which is capable of modifying a mechanical compression ratio of the internal combustion engine ; - a supercharger which is configured in order to supercharge intake air; and - a supercharging pressure adjustment mechanism which is configured in order to adjust a supercharging pressure, the internal combustion engine carrying out a fuel increment to a richer side than a stoichiometric air-fuel mixture ratio at a high supercharging pressure side, the control method comprising: - detecting (S1) the mechanical compression ratio from a device for detecting an actual compression ratio modified by the variable compression ratio mechanism ; - setting (S5) an upper limit value (L2) of the supercharging pressure on a basis of the mechanical compression ratio; and - adjusting (S7, S8, S9, S10) the supercharging pressure not to exceed the upper limit value (L2) of the supercharging pressure, the upper limit value (L2) of the supercharging pressure being within a region (R1) in which the fuel increment is carried out, wherein: - as the mechanical compression ratio becomes higher, the upper limit value (L2) of the supercharging pressure is made lower, - in a transient state in which a demand torque is raised, the control method determining a degree of pace of a rise in the demand load and adjusting the supercharging pressure not to exceed the upper limit value (L2) of the supercharging pressure in a case where the degree of pace of the rise in the demand load is abrupt, and - in a case where the degree of pace of the rise in the demand load is moderate, the supercharging pressure is adjusted not to exceed a second upper limit value (L1) of the supercharging pressure which is lower than the upper limit value (L2) of the supercharging pressure and which falls in a region (R0) in which a driving at the stoichiometric air-fuel mixture ratio is possible. - a variable compression ratio mechanism which is capable of modifying a mechanical compression ratio of the internal combustion engine ; - a supercharger which is configured in order to supercharge intake air; and - a supercharging pressure adjustment mechanism which is configured in order to adjust a supercharging pressure, - detecting (S1) the mechanical compression ratio from a device for detecting an actual compression ratio modified by the variable compression ratio mechanism ; - setting (S5) an upper limit value (L2) of the supercharging pressure on a basis of the mechanical compression ratio; and - adjusting (S7, S8, S9, S10) the supercharging pressure not to exceed the upper limit value (L2) of the supercharging pressure, the upper limit value (L2) of the supercharging pressure being within a region (R1) in which the fuel increment is carried out, - as the mechanical compression ratio becomes higher, the upper limit value (L2) of the supercharging pressure is made lower, - in a transient state in which a demand torque is raised, the control method determining a degree of pace of a rise in the demand load and adjusting the supercharging pressure not to exceed the upper limit value (L2) of the supercharging pressure in a case where the degree of pace of the rise in the demand load is abrupt, and - in a case where the degree of pace of the rise in the demand load is moderate, the supercharging pressure is adjusted not to exceed a second upper limit value (L1) of the supercharging pressure which is lower than the upper limit value (L2) of the supercharging pressure and which falls in a region (R0) in which a driving at the stoichiometric air-fuel mixture ratio is possible. <EOS>