A task management method includes determining, when a task other than an operating system task operated cooperatively with a process executed under a control of an operating system requests a cooperative operation to the operating system task and is set in a wait state, whether a priority of the task is higher than a priority of other task set in a wait state by requesting a cooperative operation to the operating system task, and making, when the priority of the task is determined to be higher than the priority of the other task, the operating system task and a process under control of the operating system operated cooperatively with the task succeed the priority of the task.