Image reading apparatus, image forming apparatus, image reading method and recording medium that ensure simplified detection of noise mixed in image signal

An image reading apparatus, comprising:

• an imaging unit that includes a valid pixel group constituted of imaging elements arranged in one row in a main-scanning direction being valid for reading a document image and dummy pixel groups constituted of imaging elements arranged on both sides of the valid pixel group being invalid for reading the document image, the imaging unit to read each line of the document image while moving relatively to a sub-scanning direction;
• and
• a noise detecting unit that detects a noise mixing into the line read by the imaging unit,
• wherein the dummy pixel group has a white data pixel group that outputs white data and a black data pixel group that outputs black data, and
• the noise detecting unit detects the noise mixing into the line when a pixel value output from the black data pixel group becomes equal to or more than a predetermined black data reference value and/or a pixel value output from the white data pixel group becomes equal to or less than a predetermined white data reference value.