Fundamental properties of a CPG using Van del Pol oscillators are examined to generate some locomotion patterns for a semi-looper-like worm robot, where such a robot adopts a locomotion of green caterpillar as a basic locomotion pattern, but sometimes it can realize a locomotion of looper. Assume that the robot is composed of simple three serial links, as a fundamental research. Several simulations are conducted for examining how to design the CPG by using inhibitory or excitory connections to obtain a stable rhythmic response, and for searching the design parameters to produce valid amount of amplitude and frequency