In Taiwan the operating model of private investigation industry has gone beyond the scope of industrial and commercial credit investigation. Nowadays private investigation industry mainly refers to private detective business that emerges to meet the social needs. Most of the cases received by private investigation companies are catching husbands with mistresses and catching couples in adultery, and private investigation companies are inevitably involved in violation of laws. But Taiwan government's attitude towards regulation of private investigation industry is not quite active. The laws promulgated in the past to regulate private investigation industry only covered industrial and commercial credit investigation, giving unclear roles to those private investigation agencies engaging in private detective business. In view of the above phenomenon that Taiwan's private investigation industry had long been illegally engaged in private detective business and constituted serious infringement of people's privacy, the Control Yuan proposed a corrective measure to the Executive Yuan and the Ministry of the Interior in 2003. Nevertheless, it has been over 10 years since the corrective measure was proposed. Up to now there is still no legal system in Taiwan concerning regulation of private investigation industry. It reveals that the government departments still does not take an active attitude towards regulation of private investigation industry, thus enabling private investigation industry to exploit legal loopholes and attain advantage in the gray area of laws. Therefore, the paper intends to refer to the related regulating legal system of the United States and Japan, and gives suggestions for improving the legal system for regulation of private investigation industry.