A fixing device includes a heating roller and a pressuring roller, a first holding member, a supporting member and a temperature detecting part. The heating roller and pressuring roller sandwiches and heats a sheet to fix a toner image formed on the sheet onto the sheet. The first holding member has a facing part facing to a circumference face of the heating roller to hold the heating roller. The supporting member is made of material with high heat resisting property as compared with the first holding member, arranged between the facing part of the first holding member and the circumference face of the heating roller so as to face to the circumference face of the heating roller, and formed in an elongated shape along an axial direction of the heating roller. The temperature detecting part is arranged in the supporting member to detect temperature of the heating roller.