The in-lane running support system includes a steering input device and a steering input detector. The in-lane running support system further comprises a reaction force device that changes a condition of the steering input device between a normal operation mode that provides a normal reaction force to the driver, and a hapthic operation mode that performs a notification operation to the driver, a turning output device that is in a state mechanically disconnected from the steering input device and that turns steerable wheels, and a turning output controller. A running state detecting device acquires information of a running state of the vehicle with respect to a lane. An in-lane running support device controls the turning output device and the haptic device based on the information of the running state such that the vehicle runs in the lane, and has a first control mode that controls the turning output control device and causes the reaction force device to operate in the normal operation mode, and a second control mode that controls the turning output control device and causes the reaction force device to operate in the haptic operation mode.