A charging device for depositing charge on a surface of a latent-image bearer of an image forming apparatus, the charging device comprising: a discharge electrode for establishing a discharge; a grid electrode arranged between the discharge electrode and the latent-image bearer; a charging power supply configured to feed, with constant current control, a charging bias Vc to be applied to the discharge electrode to deposit charge on a surface of the latent-image bearer by establishing the discharge between the discharge electrode and the latent-image bearer; a grid power supply configured to feed a grid bias V G to be applied to the grid electrode with constant voltage control; a control unit configured to perform a grid determining process, the grid determining process determining a grid setpoint value V GS, the grid setpoint value V GS being an output setpoint value for the constant voltage control of the grid bias V G; and a surface potential detector configured to output a result of detecting a surface potential V D of the latent-image bearer where charge is deposited by the discharge, characterized in that: the control unit is configured to perform a charging-current determining process, the charging-current determining process determining a charging-current setpoint value Acs, the charging-current setpoint value Acs being an output setpoint value for the constant current control of the charging bias Vc, based on a difference between the result of detection output from the surface potential detector and the grid setpoint value V GS at predetermined timing, wherein a charging-current switching value is calculated as the difference |V GS |-|V D |, wherein a first threshold of the charging-current switching value is determined in advance, wherein a second threshold of the charging-current switching value is predetermined, wherein the control unit determines that the latent image bearer has reached the end of its usable life if the charging-current switching value is equal to or larger than the second threshold, and wherein the charging-current setpoint value Acs is increased at a point in time when the charging-current switching value reaches the first threshold value and is below the second threshold value. a discharge electrode for establishing a discharge; a grid electrode arranged between the discharge electrode and the latent-image bearer; a charging power supply configured to feed, with constant current control, a charging bias Vc to be applied to the discharge electrode to deposit charge on a surface of the latent-image bearer by establishing the discharge between the discharge electrode and the latent-image bearer; a grid power supply configured to feed a grid bias V G to be applied to the grid electrode with constant voltage control; a control unit configured to perform a grid determining process, the grid determining process determining a grid setpoint value V GS, the grid setpoint value V GS being an output setpoint value for the constant voltage control of the grid bias V G; and a surface potential detector configured to output a result of detecting a surface potential V D of the latent-image bearer where charge is deposited by the discharge, characterized in that: the control unit is configured to perform a charging-current determining process, the charging-current determining process determining a charging-current setpoint value Acs, the charging-current setpoint value Acs being an output setpoint value for the constant current control of the charging bias Vc, based on a difference between the result of detection output from the surface potential detector and the grid setpoint value V GS at predetermined timing, wherein a charging-current switching value is calculated as the difference |V GS |-|V D |, wherein a first threshold of the charging-current switching value is determined in advance, wherein a second threshold of the charging-current switching value is predetermined, wherein the control unit determines that the latent image bearer has reached the end of its usable life if the charging-current switching value is equal to or larger than the second threshold, and wherein the charging-current setpoint value Acs is increased at a point in time when the charging-current switching value reaches the first threshold value and is below the second threshold value. the control unit is configured to perform a charging-current determining process, the charging-current determining process determining a charging-current setpoint value Acs, the charging-current setpoint value Acs being an output setpoint value for the constant current control of the charging bias Vc, based on a difference between the result of detection output from the surface potential detector and the grid setpoint value V GS at predetermined timing, wherein a charging-current switching value is calculated as the difference |V GS |-|V D |, wherein a first threshold of the charging-current switching value is determined in advance, wherein a second threshold of the charging-current switching value is predetermined, wherein the control unit determines that the latent image bearer has reached the end of its usable life if the charging-current switching value is equal to or larger than the second threshold, and wherein the charging-current setpoint value Acs is increased at a point in time when the charging-current switching value reaches the first threshold value and is below the second threshold value.