A numerical controller which can provide an interface that performs a safe task control for addition of an original function includes a memory management unit that develops, on a memory, a program executed by a task, an execution time calculation unit that calculates an execution time of the task, an execution condition setting unit that sets an execution condition of the task based on the results of execution of the memory management unit and the execution time calculation unit, a task monitoring unit that monitors the state of an arithmetic unit and determine the arithmetic unit to which the task is assigned, and a task control unit that registers and starts the task in the assigned arithmetic unit, based on the execution condition.