A planar light source for use in a scanning apparatus includes a light-emitting element, a first light-guiding portion and a second light-guiding portion. The light-emitting element is arranged at a side of the scanning platform opposite to the carriage module for providing a source light. The first light-guiding portion is disposed at a first side of the light-emitting element for diffusing the source light as a first planar light to be provided for a carriage module through a scanning platform of the scanning apparatus. The second light-guiding portion is disposed at a second side of the light-emitting element opposite to the first side for diffusing the source light as a second planar light to be provided for the carriage module through the scanning platform.