An image reading apparatus capable of switching between and reading a reflective original and a transparent original is adapted to consume less power and is reduced in size. The evolution of heat by a light source can be suppressed and power consumption reduced by using a solid-state light source such as an LED as light sources for illuminating both reflective and transparent originals. In addition, owing to use of LEDs and sharing of a timing drive circuit, the apparatus per se can be reduced in size.