The object of the present invention is to provide a novel developer capable or realizing a thermal recording material superior in preservation stability (i.e., heat resistance, moisture resistance) of color images and non-image areas, while satisfying the recent request for high sensitivity, and a thermal recording material using the developer. The developer for a thermal recording material of the present invention is characterized in that it consists of a composition containing, of condensates represented by the formula (I): wherein R is a halogen atom, a hydroxyl group, an alkyl group having 1 to 5 carbon atoms, an alkoxyl group having 1 to 5 carbon atoms, a cyano group, a nitro group, an aryl group or an aralkyl group, R in the number of m may be the same or different and m is an integer of 0-3, and n is an integer of 0-3, a condensate having two cores wherein n=0 as a main component, and at least one kind of condensate of the formula wherein n=1-3, and that a thermal recording material obtained using this developer shows high sensitivity, high dynamic color density, and superior preservation stability.