A thermally color-developing reversibly thermochromic pigment which shows a uniform color density in the coloring temperature range and also shows an optimal .DELTA.H value within a range of from 3 to 40.degree. C. Thermally color-developing reversibly thermochromic pigments of a three component system having a .DELTA.H value within a range of from 7 to 40.degree. C. in which at least essential three components including (a) an electron-donating chromic organic compound, (b) a specified compound selected from the gallic acid esters and (c) a reaction medium selected from alcohols, esters, ketones and hydrocarbons; which reversibly generates color reactions of both of the compounds within a specified temperature range and has a melting point of less than 50.degree. C., are microencapsulated, and of a four component system having a .DELTA.H value within a range of from 3 to 25.degree. C. in which a compound (d) selected from monomer compounds having a melting point of 50.degree. C. or more or polymer compounds having a softening point of 70.degree. C. or more is added to the three component system.