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: executing a first plurality of commands in the first computer according to an execution order; executing a second plurality of commands in the second computer according to the execution order; storing configuration information of a migration source that includes one or more parameters generated by executing the first plurality of commands and the second plurality of commands in the system, the one or more parameters being used for executing unexecuted commands among the first plurality of commands and the second plurality of commands in the target system; executing a command among the first plurality of commands and the second plurality of commands in the target system; generating configuration information of a migrating destination that includes the one or more parameters generated by executing the command; selecting, by referring to the configuration information of the migrating source and the configuration information of the migrating destination, 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; executing the selected command on the target system; and updating the configuration information of the migrating destination based on a result of the executing of the selected command.