A task execution method for executing a plurality of tasks while switching the tasks from one to another by time-sharing, wherein an allocated time is allocated for each of the plurality of tasks, and the plurality of tasks includes a plurality of first-type tasks and a single second-type task, and the task execution method includes a task selection step which selects a task from among the plurality of tasks according to a predetermined sequence, a correction step which corrects an allocated time for the second-type task so that execution of the plurality of tasks completes within the cycle time, when the task selected is a second-type task, which is the total allocated time for the plurality of tasks, and a task execution control step which causes the selected task to be executed so that the execution of the selected task completes within the allocated time or the corrected allocated time.