The sheet material identification apparatus, includes a sensor adapted to bring a probe having a built-in piezoelectric element into contact with a surface of sheet material being conveyed, and thereby to generate electric detection signals corresponding with irregularities of the sheet material surface; an identification part adapted to identify types of sheet material based on detection signals outputted from the above described sensor; and a correct part adapted to correct fluctuations in detection features of the above described sensor based on detection output of the above described sensor at the time when the above described sensor has detected correction sheet material having a predetermined surface roughness. The appratus prevents misdetection during use for a long period of sheet material identification apparatus that does not require any type-of-paper selection setting operation by a user and can implement good heat treating, fixing and image forming efficiently even if sheets of paper having various kinds of surface roughness.