A systematical field survey applied Conjoint Analysis (CA) concerned on two specified social issues; global warming and heat island problems is conducted. We applied the so-called web-site survey to secure both quantity and quality of a series of acquired data sets. Both obtained Marginal Willing to Pay (MWTP) for the global warming and heat island issues seems plausible. Interestingly, it is observed an evident tendency that younger subjects incline to pay more than older subjects, which implies younger people paying much attention to the environmental issues. We found that the level range of payment in a questionnaire significantly affects MWTP, which means how design a payment range would bring considerable bias in some cases. Also a principle problem whether a subject's payment was questioned by explicit as a form of additional payment to the public or implicit as a form of re-allocation of already-collected tax from the people, is observed significantly influential in the MWTP. The result also suggests that three-choice type CA seems better than pairwise type CA to obtain plausible MWTP when a questionnaire relates to a certain ideal issue that is difficult for subjects to understand its trade-off structure in proper way.