We have mapped 1 deg2 region toward a high latitude HII region S73 (l, b) = (37°.69, 44°.55) and associated molecular cloud in 12CO J = 1 - 0, and 13CO J = 1 - 0, using the 3 mm SIS receiver on the 14 m telescope at Taeduk Radio Astronomy Observatory. A high resolution autocorrelator is used to resolve extremely narrow CO linewidths (FWHP < 1 km/s) of the molecular cloud. Though the linewidths are very narrow, it is found that there is systematic velocity gradient in the molecular gas associated with the H II region. Both of 12CO and 13CO averaged spectra are non-gaussian, and there are obvious blue wings in the spectra. It is remarkable that the linewidths at the blueshifted region are broader than those of the rest of the cloud. The CO emission does match well with the dust emission.