MOBILE OBJECT CONTROL DEVICE, MOBILE OBJECT CONTROL METHOD, AND STORAGE MEDIUM

Provided is a mobile object control device including: a storage medium having computer-readable instructions stored therein; and a processor connected to the storage medium, wherein the processor executes the computer-readable instructions, to thereby recognize a surrounding situation of the mobile object on the basis of an output of a detection device that detects the surrounding situation of the mobile object, enable any of a plurality of modes including a startup mode in which a lane change system is started up by an occupant's operation of the mobile object and a control mode in which lane change control of the mobile object is performed in a case where a lane change start condition is satisfied after the startup mode is started up, determine whether the mobile object has reached within a predetermined range from a lane change section on the basis of at least one of the recognized surrounding situation and map information, determine whether the lane change start condition has been satisfied after the startup mode is started up, and determine whether the mobile object has passed through the lane change section, perform the lane change control in a case where it is determined that the mobile object has reached within a predetermined range from the lane change section after the startup mode is started up and that the lane change start condition has been satisfied, and stop the startup mode in a case where it is determined that the mobile object has reached within a predetermined range from the lane change section after the startup mode is started up and the lane change start condition is not satisfied, and then restore the startup mode in a case where it is determined that the mobile object has passed through the lane change section.