To provide a method and a device for charge control agent density for the liquid developer, capable of directly detecting precisely the density of a charge control agent in the liquid developer with toner and the charge control agent in dispersed carrier liquid without being affected by the toner charge quantity and the toner density, and precisely controlling the density of the charge control agent in the liquid developer with toner and the charge control agent dispersed in the carrier liquid to a specified density.

This charge control agent density detecting device 50 capable of executing the method, for detecting the density of the charge control agent in the liquid developer D produced by dispersing the toner and the charge control agent in the carrier liquid, is allowed to find out the charge control agent density in the developer D based on measured potential, by arranging the developer D between a roller electrode 51 and counter electrode 53 (two electrode), sticking the toner in the developer D on the roller electrode 51 by applying a specified voltage between both electrodes, and making the potential saturated by the static charge in the developer D, and then measuring the positional of the toner sticking surface of the roller electrode 51 by arranging the toner sticking surface in a non-electric field applying area P0.