A heating blade unit, a treatment tool, and a method of manufacturing a heating blade unit are disclosed. The heating blade unit includes: an electric heater, a blade, and a cover made of a thermosetting resin. The blade includes a treatment surface, an installation surface that is provided on a side opposite to the treatment surface and on which the electric heater is installed, and a support surface that is provided at a position different from a position at which the installation surface is provided. The cover integrally covers the electric heater, and one or more surfaces of the blade.