Tribo-charging characteristics on toner in a two-component developer are affected by various factors such as material component, shape, and methods of tribo-charging or measuring. A negative yellow type of pulverized toner is used as a sample, and the material is based on bisphenol A and polyester resin. Tribo-charging treatment is performed by using a developed mixing shaker with arm length of 200 mm. Charge to mass ratio q/m is measured by the E-SPART method. From the experimental results, it is shown that the q/m varies unstably and fluctuates with shaking time within 5 min, but the q/m changes gradually to a constant value of −13.5 μC/g at 20 min after 4 min for the 5 wt% of toner concentration. In order to investigate the change of the q/m, the observation via SEM on toner particles after the shaking treatment is performed. The q/m dependence on toner concentration from 1 wt% to 10 wt% in the developer is also reported.