An integrated simulation system includes a first simulation device which executes a simulation of a first program, a second simulation device which executes a simulation of a second program, a start timing setting section which sets start timing for the correlated first program and second program so as to verify the presence or absence of malfunctions caused by a start order of the correlated first program and second program, and a program starting section which issues commands to the first simulation device and the second simulation device to start the correlated first program and second program at the set start timing by a single starting operation.