A toner binder comprising a crosslinked polyester resin obtained by using 0.1 to 3 mol % of trimellitic acid and 0.1 to 5 mol % of an epi-bis type epoxy in combination as crosslinking components, said binder having a number average molecular weight (Mn) in the chromatogram determined by a gel permeation chromatography on the non-gel portion of the polyester resin, of 2,000 to 4,000, a ratio (Mw/Mn) of the weight average molecular weight to the number average molecular weight of 10 to 25 and a (percent gel) of the residue unsoluble in tetrahydrofuran solvent of 1 wt % or less. A toner composition for flash fixing comprising the above-described binder as an essential constituent component. The toner and the toner binder exhibit good fixability and void resistance upon flash fixing and produce little fixing odor.