This research is an exploratory study to inquire into the causes of gambling crime of professional gambler, taking interview as the research strategy, selecting cases by ”Typical-cases Sampling” and ”Reputation-cases Sampling”. This research selects policemen who have abundant experience in detecting gambling cases, and people who have been running illegal casino. This In-depth interview asks three kinds of questions, including the generalization items, detail items, and evaluation items. The research discovered that most professional gamblers are low S.E.S., over 30 years old, jobless or gangster-background male; the female then are housewife or females who working in the erotic club. Their life style are ”Day sleep; night bet”, often keep late hours about 3 or 4p.m. The formation which commits gambling crime is the person who possess specific demography characters and special psychological characters, such as to pursue excitements, strong speculation, ...and so on, which attracted by gambling behavior for the frequently contact in their growth process. These people became the professional gambler in entering the society or after backing from military service, and most actively participating illegal gambling approximately at 3050 years old period. Most of the professional gamblers are low social stratum, having some special psychological characteristics of low self-control, and their living are extremely unstable. Their life styles are at variance with the ordinary civilian's, and their conducts have no contribution to the society. The professional gamblers cannot do any huge harm to the society, if compared with the serious crime. This discovery is meaningful to the present gambling criminal policy.