The two-dimensional assemblies of the circular rods made of epoxy resin are tested in a two-dimensional simple shear apparatus. Magnitudes and directions of interparticle forces and directions of effective contact planes are measured by using the photoelastic method. Relationships between the variations of distribution of these microscopic quantities and macroscopic behaviour of the assemblies are inevestigated. The distribution of directions of contact planes varies with the shear strain. But the direction of the interparticle force depends on the direction of the contact plane. Because the angles of mobilized inter particle friction concentrated at zero degree, the distribution of directions of contact planes are not so different from tha...