To simultaneously satisfy the improvement of fuel consumption and the control of output reduction during the application of a high load so as to secure driving performance requested by a driver.

A normal Otto cycle is adopted for two cylinders #2 and #3 selected from the four cylinders #1 to #4 of an engine 1, a so-called Atokinson cycle is used for the remaining two cylinders #1 and #4 and a cam profile is set so as to close air intake valves corresponding to the cylinders #1 and #4 with a timing slower than that a normal timing. When the load of the engine 1 is in a low load region, a real compression ratio in the cylinders #1 and #4 is smaller than an expansion ratio and thus at least in the cylinders #1 and #4, thermal efficiency is increased. Also, in a high load region, a real compression ratio is equal to an expansion ratio in the two cylinders #2 and #3 and a normal combustion state is secured. Thus, the output of a requested is secured.