A toner is provided which is excellent in low-temperature fixability and offset resistance, has a wide fixing temperature range, provides fixed images with high gloss, and can form toner images having high quality. The toner is composed of toner particles having toner base particles each containing a binder resin and a colorant. When the viscosities of each of the toner particles measured at 100.degree. C. and 110.degree. C. by a flow tester heat-up method are represented by .eta..sub.100 (Pas) and .eta..sub.110 (Pas), respectively, an average variation in viscosity A.sub..eta.T represented by the following equation (1) satisfies the relationship of 0.gtoreq.A.sub..eta.T.gtoreq.-0.064: A.sub..eta.T=(log(.eta..sub.110)-log(.eta..sub.100)/(110-100); and (1) .eta..sub.100 is 15,000 to 40,000 Pas.