DECELERATION SUPPORT DEVICE

A control unit is a deceleration support device configured to execute an automatic deceleration control that automatically decelerates an own vehicle until an index value acquired by dividing an inter-vehicle distance between a preceding vehicle and the own vehicle by a relative speed of the own vehicle with respect to the preceding vehicle becomes equal to or greater than an end standard value, when the index value is equal to or less than a start standard value, and when the inter-vehicle distance is equal to or less than a control start distance standard value, in a situation in which a preset permission condition is established. When the traveling mode is an eco mode that reduces energy required for travel, the control unit sets the control start distance standard value to a value for the eco mode that is larger than a standard value for a normal mode.