Swarm robotics is a research area which aims for coordination of large numbers of robots. One of the design methods for swarm robotic systems is the use of evolutionary robotics approach. In evolutionary robotics approach, evolution process often carries out in simulation due to the large amount of time required to obtain the desired collective behavior. The behavior of real robots, however, tends to vary from the one in simulation. This problem is known as the reality gap, which is one of the major issues in evolutionary robotics. This paper focuses on how the individual-level simplicity affects the reality gap of the swarm-level behavior. By changing the resolution capability of sensory inputs, preferable specification of robot's sensors are investigated which is effective to reduce the reality gap.