We measured the X-ray polarization using our micro-pixel chamber with a strip readout, while changing the X-ray energy (5- 18 keV) and gas mixtures (neon- and argon-based). As a result, modulation factors of 0.18 (at 9 keV) and 0.12 (at 14 keV) were obtained for neon- and argon-based mixtures, respectively. We also simulated this experiment utilizing a Monte-Carlo code, EGS4, which reproduced the experimental results quite well. According to the Monte-Carlo simulation, the modulation factor should be improved by a pixel-readout detector. The simulated modulation factors are 0.25 (for X-ray with energy at >6 keV) with a neon-based gas mixture and 0.18 (for X-ray at >10 keV) with an argon-based one.