Abstract: In an electrostatic image developing device for electrical photocopiers, a magnetizable one-component toner, initially contained in a removable container, is fed, by the action of a rotating flexible strip, through a development chamber towards a rotating non-magnetic development roller surrounding a number of stationary permanent magnets, forming on it a magnetic brush, whose thickness is controlled by a non-magnetic flexible blade pressed against the surface of the development roller; the development chamber is fitted with three stirring bars made of non-magnetic material, each bar describing a different closed path in different zones of the development chamber in such a way as to avoid the formation of lumps and to maintain the correct fluidity of the toner. In addition, a metallic wire is fitted in the development chamber and acts as a sensor device to detect when the removable container is nearly empty of toner.