A positively chargeable toner includes a plurality of toner particles each including a core and a shell layer disposed over a surface of the core. The core contains a polyester resin. The shell layer covers at least 40% and no greater than 80% of an area of the surface of the core, ζ(4) is greater than 0 V. ζ(6) is less than 0 V. A relationship represented by |ζ(3)−ζ(4)|>|ζ(6)−ζ(7)| is satisfied. ζ(3), ζ(4), ζ(6), and ζ(7) represent zeta potentials of the positively chargeable toner with the toner particles having no external additive. ζ(3), ζ(4), ζ(6), and ζ(7) are respectively measured in an aqueous medium at pH 3, pH 4, pH 6, and pH 7.