To provide a setter for substrate heat-treating inexpensively carrying out heat treatment while keeping a large TFT substrate or the like in a high degree of cleanliness; and a method of heat-treating a TFT substrate using the same.

This setter for substrate heat-treating includes: a setter body 1 using the circumference of a flat body as a frame-like sealing frame 3, and using its inside part as a housing part of a glass substrate 10 with a functional film formed on an upper surface thereof; and a flat setter lid 2 mounted on its upper surface and tightly fitted to the sealing frame 3. When the setter is used, heat treatment can be carried out in a clean condition even if an existing PDP baking furnace is used. The setter lid body 2 can be reinforced by a flexure-preventing beam located on the upper or lower surface thereof.