We conducted CO J=1→0 emission line observations for nearby AGB stars using the Nobeyama 45 m telescope. Comparing our results with those from CO J=3→2 observations with JCMT, the circumstellar envelopes observed in CO J=1→0 look more extended than J=3→2. Thus, we could trace the outer, cold parts of the envelopes. We also found four stars in which the CO/13CO ratio changes dramatically outward, but the change implies the effect of selective photodissociation by interstellar ultraviolet radiation, not the third dredge up in the stellar interior. We moreover found two unique stars with aspherical envelope morphology.