Yamaichi Securities Co. formally decided Monday to close down voluntarily amid a financial crisis linked to flagging stock prices, fallen credibility from payoff scandals and recently discovered losses from illegal "tobashi" trading activities.

The firm, one of the nation's Big Four brokerages, filed for voluntary closure Monday morning with the Finance Ministry, terminating 100 years of business. The ministry instructed Yamaichi to suspend the initiation of all new transactions.

The downfall of Tokyo-based Yamaichi is projected to leave behind roughly 3 trillion yen in unresolved debts, making it the largest corporate failure in Japanese history. Debts of the entire Yamaichi group are reported to have reached 6.7 trillion yen.