An input apparatus, a control apparatus, a control system, and a control method therefor, that are capable of solving a problem on gravity that affects an acceleration sensor of an input apparatus when tilted from its original position, and reducing a calculation amount are provided. An MPU of an input apparatus corrects angular velocity values by rotational coordinate conversion corresponding to a calculated roll angle to obtain correction angular velocity values (second and first correction angular velocity values) as correction values. Accordingly, even when a user moves the input apparatus in a state where the input apparatus is tilted with respect to an axis in a gravity direction (vertical axis) about a Z axis, effects of gravity acceleration components in X′- and Y′-axis directions that are generated by the tilt can be removed.