We present the results of ALMA spectroscopic follow-up of a z = 6.766 Ly alpha emitting galaxy behind the cluster RX J1347.1-1145. We report the detection of [C II] 158 mu m line fully consistent with the Ly alpha redshift and with the peak of the optical emission. Given the magnification of mu = 5.0 +/- 0.3, the intrinsic (corrected for lensing) luminosity of the [C II] line is L[C II]= 1.4(-0.3)(+0.3) x 10(7) L-circle dot, roughly similar to 5 times fainter than other detections of z similar to 7 galaxies. The result indicates that low L[C II] in z similar to 7 galaxies compared to the local counterparts might be caused by their low metallicities and/or feedback. The small velocity offset (Delta v = 20(-40)(+40) km s(-1)) between the Ly alpha and [C II] line is unusual, and may be indicative of ionizing photons escaping.