An image capturing device that detects a change in lane width for a vehicle without using information on an adjacent lane is mounted in the vehicle and includes a first camera which captures a first image and a control device which recognizes, in the first image, first and second compartment line L1 and L2 that regulate lanes. The control device determines the presence or absence of a change in lane width on the basis of relationships among the widths of the first compartment line L1 at two points PV1, PV2 at which the distances from a vehicle on the first image are different, the widths of the second compartment line L2 at the two points PV1, PV2 on the first image, and the distances between the first compartment line L1 and the second compartment line L2 at the two points PV1, PV2 on the first image.