A failure diagnosis apparatus for a throttle valve actuating device is disclosed. The throttle valve actuating device has an actuator for actuating a throttle valve provided in an intake system of an internal combustion engine and biasing elements for biasing the throttle valve to a predetermined retention opening. A feedback control of the throttle valve is performed so that an opening of the throttle valve coincides with a first predetermined opening. After the throttle valve is controlled to the first predetermined opening, a feedback control of the throttle valve is performed so that an opening of the throttle valve coincides with a second predetermined opening. It is determined that the throttle valve actuating device has failed when the time period during which the opening of the throttle valve remains in a predetermined determination range including the second predetermined opening, is shorter than a predetermined time period when performing the feedback control to the second predetermined opening.