A fuser having a heater, a belt, and a holder, is provided. The heater includes a metal-made base plate and a resistive-heating element and has a first face and a second face. The resistive-heating element is formed on at least one of the first face and the second face. The belt being an endless belt has an inner circumferential surface contacting the first face of the heater and rotates around the heater. The holder has a retainer face to contact the second face of the heater to retain the heater and a belt-guiding face to contact the inner circumferential surface of the belt and guide the belt there-along. The base plate has a pair of first edges located on one end and the other end of the first face in the widthwise direction extending in the lengthwise direction. The pair of first edges are rounded at ridges.