A mounting structure for an inverter circuit board for a light source lamp of an image reader in which mounting means for mounting the inverter circuit board for a light source lamp of an image reader onto a carriage is located to be operated from the direction in which the carriage moves in one embodiment. The inverter circuit and heat dissipation plate are removably mounted to an end of the full rate carriage. In another embodiment, the circuit board is mounted to the top for access from above the carriage.