1. An execution control method performed by a processor in migrating a system including a first computer and a second computer to a target system including a third computer and a fourth computer, the execution control method comprising: storing a first plurality of commands executed in the first computer and a first execution order of the first plurality of commands, the first execution order indicating an execution order according to which the first plurality of commands are to be executed on the third computer; storing a second plurality of commands executed in the second computer and a second execution order of the second plurality of commands, the second execution order indicating an execution order according to which the second plurality of commands are to be executed on the fourth computer; storing configuration information generated by executing commands among the first plurality of commands and the second plurality of commands, the configuration information used to execute unexecuted commands among the first plurality of commands and the second plurality of commands; selecting, using the stored configuration information, a command which is executable on the target system from a first earliest command that is at an earliest position in the first execution order among unexecuted commands of the first plurality of commands on the third computer and a second earliest command that is at an earliest position in the second execution order among unexecuted commands of the second plurality of commands on the fourth computer; and executing the selected command.