CONTROLLER AND CONTROL METHOD FOR RIDER-ASSISTANCE SYSTEM OF STRADDLE-TYPE VEHICLE

The invention obtains a controller and a control method capable of improving assistance performance for a rider. A controller for a rider-assistance system of a straddle-type vehicle () includes an execution section executing rider-assistance operation to assist a rider of an own vehicle () on the basis of positional relationship information between the own vehicle () and a target, and further includes an acquisition section acquiring positional information of the own vehicle () in a group in the case where a group travel mode as a mode in which a group formed of plural straddle-type vehicles (), including the own vehicle (), travel in plural vehicle lines (C C) in a single lane (L) is determined to be valid. In the case where it is determined that the group travel mode is valid, the execution section executes the rider-assistance operation on the basis of the positional information acquired by the acquisition section.