Molecular dynamic simulation is used to investigate the atomic mechanism of dynamic friction behavior associated with the atom arrangement utilizing the soft-core potential for the contact surfaces. The Johnson potential is used for α-iron single crystal bulk in an elastic contact condition. The effect of the shape of the soft-core potential is examined, and the resulting thermal distribution is discussed. A frictional model is composed of two specimens, an upper one and a lower one. As the upper specimen slides along the lower in one direction, atomic friction force is generated. The dynamic friction force is evaluated at the point of decreasing slip velocity. The results are summarized as follows : ( 1 ) An increase in the load applied to the contact surface raises the temperature of the contact surface. ( 2 ) The coefficient of dynamic friction calculated by the friction force generated at the contact surface is decreased due to the increasing core-radius of the soft-core potential. It remains almost constant regardless of variation in the load.