We measured the electric conductivity of a carbon particle bed from the static to the fluidized state by using single-size carbon particles within the range of 66 mum similar to 490 mum and a two-component system in which 17 mum fine particle carbons were added to the single size system, and examined the effects of gas velocity, particle size and fine particle addition on the conductivity. The electric resistance of the bed showed the S-shape dependency on the gas velocity, with a significant increase near the minimum fluidization velocity. The conductivity of the single-size system was of similar magnitude regardless of the particle size. On the other hand, the conductivity of the two-component system became one order of magnitude higher than that of the single-size system. The void generation in the bed for each particle system was characterized by the curve of the particle fraction ratio, (1 - epsilon) / (1 - epsilon(0)), and the conductivity ratio, sigma(b)/sigmab(0).