An alarm system for a vehicle, comprising: an alarm line setting part configured to set an alarm line (61, 62) that extends forward from the vehicle (2 in a longitudinal direction of the vehicle; an object detection part configured to detect an object on a side of the vehicle; a collision determination part configured to determine whether or not the object crosses the alarm line (61, 62) within a predetermined time; an alarm unit control part configured to activate an alarm unit when the collision determination part determines that the object crosses the alarm line (61, 62) within the predetermined time; and a left/right-turn determination part configured to determine that the vehicle is to turn left or right at an intersection, wherein, provided that, when the vehicle enters the intersection, of a plurality of lanes at the intersection that intersect with a lane in which the vehicle is running, a lane closer to the vehicle is defined as a first lane, and an opposing lane to the first lane that is further from the vehicle is defined as a second lane; the alarm line setting part is configured to set a length of the alarm line (61, 62) at a first length when the vehicle is running in a straight line; and the alarm line setting part is configured to set the length of the alarm line (61, 62) at a length different from the first length when the vehicle is to turn left or right at the intersection to enter the first lane or the second lane, wherein the alarm line setting part is configured to set, as the alarm line (61, 62), a right alarm line for an object on a right side and a left alarm line that is set for an object on a left side independently from the right alarm line; the alarm line setting part is configured to set the length of the right alarm line at the second length when the vehicle is to turn right at the intersection to enter the first lane; and the alarm line setting part is configured to set the length of the left alarm line at the second length when the vehicle is to turn left at the intersection to enter the first lane, characterized in that the alarm line setting part is configured to set the length of the left alarm line at a third length longer than the first length when the vehicle is to turn right at the intersection to enter the first lane; and the alarm line setting part is configured to set the length of the right alarm line at the third length when the vehicle is to turn left at the intersection to enter the first lane. an alarm line setting part configured to set an alarm line (61, 62) that extends forward from the vehicle (2 in a longitudinal direction of the vehicle; an object detection part configured to detect an object on a side of the vehicle; a collision determination part configured to determine whether or not the object crosses the alarm line (61, 62) within a predetermined time; an alarm unit control part configured to activate an alarm unit when the collision determination part determines that the object crosses the alarm line (61, 62) within the predetermined time; and a left/right-turn determination part configured to determine that the vehicle is to turn left or right at an intersection, wherein, provided that, when the vehicle enters the intersection, of a plurality of lanes at the intersection that intersect with a lane in which the vehicle is running, a lane closer to the vehicle is defined as a first lane, and an opposing lane to the first lane that is further from the vehicle is defined as a second lane; the alarm line setting part is configured to set a length of the alarm line (61, 62) at a first length when the vehicle is running in a straight line; and the alarm line setting part is configured to set the length of the alarm line (61, 62) at a length different from the first length when the vehicle is to turn left or right at the intersection to enter the first lane or the second lane, wherein the alarm line setting part is configured to set, as the alarm line (61, 62), a right alarm line for an object on a right side and a left alarm line that is set for an object on a left side independently from the right alarm line; the alarm line setting part is configured to set the length of the right alarm line at the second length when the vehicle is to turn right at the intersection to enter the first lane; and the alarm line setting part is configured to set the length of the left alarm line at the second length when the vehicle is to turn left at the intersection to enter the first lane, characterized in that the alarm line setting part is configured to set the length of the left alarm line at a third length longer than the first length when the vehicle is to turn right at the intersection to enter the first lane; and the alarm line setting part is configured to set the length of the right alarm line at the third length when the vehicle is to turn left at the intersection to enter the first lane.