A simulator capable of counting a number of events occurring in each of functional modules constituting an LSI and calculating an index value for selecting a simulation method for each functional module in simulation of an operation of the LSI with a first test vector set. The simulator further capable of selecting one simulation method among a plurality of simulation methods for each functional module based on the selection index value, and of controlling execution of simulation of the LSI operation with a second test vector set in the simulation method selected for each functional module.