A magnetic marker (1), laid in or on a road so as be detectable by a magnetic sensor (2) attached to a bottom surface side of a vehicle (5), that is used for vehicle-side drive assist control for assisting driving is an isotropic ferrite plastic magnet, molded into a columnar shape, that contains a magnetic powder of iron oxide, i.e. a powder of a magnetic material, dispersed in a polymer material. In a marker system (1S) including this magnetic marker (1), magnetic markers (1) accommodated in holes (530) bored in a road surface (53) are arranged along the center of a lane.