Patent ID: 8577232

Claim:
A thermal fixing device, comprising: a fixing member; a flexible endless belt disposed on an outer circumferential surface of the fixing member; a rotary pressure member disposed parallel to and pressing against the fixing member via the endless belt; a heating unit to heat the endless belt; and a rotation detector to detect a rotation speed of the endless belt, wherein the heating unit is powered off when the rotation speed of the endless belt detected by the rotation detector is at or below a predetermined threshold value, wherein the rotation detector comprises a rotary member rotated by rotation of the endless belt, and detects the rotation speed of the endless belt based on rotation of the rotary member, and wherein the rotary member comprises an auxiliary roller disposed away from the endless belt and a rotary belt looped around the auxiliary roller and the outer circumferential surface of the endless belt outside the area of maximum image size in the axial direction of the endless belt.