Patent ID: 7885559

Claim:
A light amount measuring device configured to be used to in an image forming device where the light amount measuring device receives light reflected from an image with a density patch and the image forming device adjusts a density of toner based on the light detected by the light amount measuring device, the light amount measuring device comprising: a light-receiving sensor having an output terminal and capable of outputting a voltage corresponding to an amount of incident light from the output terminal, the light-receiving sensor being located to receive light reflected from the density patch; an A/D converting portion having an input terminal and capable of converting an input voltage input from the input terminal into a digital value; a light amount calculating portion capable of calculating the amount of light incident on the light-receiving sensor on the basis of the digital value obtained by conversion by the A/D converting portion; a resistor connected between the A/D converting portion and the light-receiving sensor, one end of the resistor being connected to the input terminal of the A/D converting portion and another end of the resistor being connected to the output terminal of the light receiving sensor; and a zener diode having one end connected between the input terminal of the A/D converting portion and the resistor, wherein the zener diode is capable of allowing a breakdown current flow from the one end to another end if an output voltage from the light-receiving sensor is not less than a predetermined value.