The authors used a simple model and a prototype machine to study statics and dynamics of a magnetic brush in a two-component development system in electrophotography. In the model experiment, the authors measured the normal and tangential forces of the brush formed from a chain of magnetic carrier particles when it comes in contact with the photoreceptor to clarify the relationship between the tangential friction force and the diameter of the carrier particles, magnetic flux density, and the length of the brush. The tangential friction force increased with the magnetic flux density and decreased with an increase in the length of the brush; however, the total force was unaffected by the diameter of the carrier particles. On the other hand, numerical calculations performed using an improved distinct element method revealed that although the total force was not affected by the diameter of the carrier particles, the individual differential force acting on the magnetic particles of the chain was small, and the density of the carrier particles that come in contact with the photoreceptor drum was high when the size of the particles was small. In the investigation carried out using the prototype machine, it was found that the magnetic brush formed in the development area is inclined in a direction parallel to the magnetic field and that the chains are crushed by the photoreceptor drum. Although the total pressure applied on the photoreceptor was almost independent of the diameter of the carrier particles, the differential force exerted by individual chains is small and distributes dense when the size of the particles is small; on the other hand, it is large and distributes rough when the size of the particles is large as predicted by the model investigation. This result suggests that small carrier particles are advantageous in preventing any disturbances in the images developed on the photoreceptor. The effects of the development gap and the thickness of the layer of supplied carrier particles have also been evaluated.