Kyoei Life Insurance Co., a troubled midsize insurer with liabilities of about 4.5 trillion yen, filed for protection from creditors with the Tokyo District Court on Friday, making it the largest life insurer to collapse since World War II, company officials said.

The failure, ranked 11th in asset terms on Kyoei's 4.6 trillion yen, comes only 11 days after Chiyoda Mutual Life Insurance Co. -- 12th in asset terms at 3.5 trillion yen -- filed for court protection with 2.9 trillion yen in liabilities.

Like Chiyoda, Kyoei has invoked fast-track legislation aimed at rehabilitating troubled financial institutions.