1. A method for controlling a program execution device which includes a plurality of debuggers and a program execution unit, the program execution unit executing, in parallel, a plurality of programs to be debugged by the debuggers, said method comprising: receiving a start request to start program execution or a stop request to stop program execution from each of the debuggers, and holding a flag indicating the start request or the stop request for each of the debuggers; and causing the program execution unit to start or stop executing the programs, based on a combination of the start request and the stop request indicated by the flags, wherein, in said causing, when the program execution unit is caused to stop executing the programs, the stopping of the execution of the programs is notified to a debugger included in the debuggers and corresponding to the flag indicating the stop request.