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We present a Giant Molecular Cloud (GMC) catalog toward M33, containing 71GMCs in total, based on wide field and high sensitivity CO(J=3-2) observationswith a spatial resolution of 100 pc using the ASTE 10 m telescope. Employingarchival optical data, we identify 75 young stellar groups (YSGs) from theexcess of the surface stellar density, and estimate their ages by comparingwith stellar evolution models. A spatial comparison among the GMCs, YSGs, andHII regions enable us to classify GMCs into four categories: Type A showing nosign of massive star formation (SF), Type B being associated only with HIIregions, Type C with both HII regions and <10 Myr-old YSGs and Type-D with bothHII regions and 10--30 Myr YSGs. Out of 65 GMCs (discarding those at the edgesof the observed fields), 1 (1%), 13 (20%), 29 (45%), and 22 (34%) are Types A,B, C, and D, respectively. We interpret these categories as stages in a GMCevolutionary sequence. Assuming that the timescale for each evolutionary stageis proportional to the number of GMCs, the lifetime of a GMC with a mass >10^5Mo is estimated to be 20--40 Myr. In addition, we find that the dense gasfraction as traced by the CO(J=3-2)/CO(J=1-0) ratio is enhanced around SFregions. This confirms a scenario where dense gas is preferentially formedaround previously generated stars, and will be the fuel for the next stellargeneration. In this way, massive SF gradually propagates in a GMC until gas isexhausted.

GMC Evolutions in the Nearby Spiral Galaxy M33