The present invention is the thermally sensitive recording medium comprising a thermally sensitive color developing layer containing colorless or pale colored basic leuco dye and a color developing agent as a main components on a substrate, wherein said thermally sensitive recording layer contains acrylic emulsion and colloidal silica, further contains at least one kind of diphenylsulfone bridgeable compound represented by general formula A as the color developing agent, ##STR00001## wherein, X and Y can be different or same and indicates a saturated or an unsaturated liner or grafted hydrocarbon group of carbon number 1 12 which can possess an ether bond, or indicate, ##STR00002## wherein, R indicates a methylene group or an ethylene group, T indicates a hydrogen atom or an alkyl group of carbon number 1 4, and R.sub.1 R.sub.6 independently indicate a halogen-atom, an alkyl group of carbon number 1 6, or an alkenyl group, further, m, n, p, q, r, t indicate an integer number of 0 4 and when are bigger than 2, R.sub.1 R.sub.6 can be different, and a is an integer of 0 10.