An image scanner includes first and second carriages, a body, a power source, a power supplier, and a tensioner. In the first carriage moving at a predetermined speed, a light source emits light onto an original. A first mirror deflects the light reflected by the original. In the second carriage moving at a half speed of the first carriage, second and third mirrors deflect the light deflected by the first and second mirrors, respectively. The body holds the first and second carriages. The power source drives the light source. The power supplier is connected to the power source and the light source to supply power from the power source to the light source. The tensioner provided on the second carriage contacts the power supplier at a position outside an optical light path and applies tension to the power supplier.