An image reading apparatus of a contact image sensor type includes an area light source. The image reading apparatus is used for reading a light transmitting original placed on an original base by irradiating light thereto from the area light source and receiving transmission light. The original base has an uneven portion on a front surface on the side on which the light transmitting original is placed so that the adhesion of the light transmitting original to the original base is prevented upon placing the light transmitting original on the original base. The uneven portion does not effect optical characteristics for reading the light transmitting original.