Provided is a heater that is excellent in heat equalizing property even when being narrow in a sweep direction. Also provided are a fixing device, an image-forming device, and a heating device each including such a heater. A heater is configured to heat an object to be heated in such a manner that at least one of the object to be heated and the heater is swept with the heater disposed opposite the object to be heated. The heater includes a base having a rectangular shape and a plurality of heating cells each independently receiving power supply, the heating cells being disposed on the base and arranged in a longitudinal direction of the base. Each of the heating cells includes a plurality of lateral wires extending in substantially parallel with the longitudinal direction of the base and a plurality of oblique wires tilted relative to the lateral wires.