Toshihiko Mizuno was caught in Tokyo yesterday on suspicion of "habitual indecency," which carries a penalty of up to one year in jail or a fine of one million yen (USD12,400), the Metropolitan Police Department said.
Mizuno separately approached the three girls, aged nine and 10, in October and December last year outside apartment towers or in the street, saying: "I am doing research on saliva. Give me your saliva," an MPD spokesman said.
"He videotaped them as they spat out saliva. He also asked them to open their mouths and filmed their mouth interiors and tongues," the official said. "He has done so habitually to satisfy his sexual desire."
Media reports, quoting police sources, said that Mizuno had approached about 4,000 young girls and managed to collect saliva from about 500 of them over 17 years in Tokyo and neighbouring Saitama.
Police have found 26 videotapes at his home showing more than 200 girls, the Jiji and Kyodo news agencies said.
The MPD official could not confirm the media reports.