Japan Post Insurance, 64% owned by Japan Post Holdings, first revealed it had mismanaged insurance policies affecting thousands of clients in August.
Japan's financial regulator then in December ordered Japan Post Insurance to stop marketing insurance policies, which were sold at outlets of postal service unit Japan Post, until March.
"We do not have any guidance for when we can resume sales. Our mission now is to carry out what we have pledged in our business improvement plans," Masuda told at a media briefing.
He spoke after the group submitted the business improvement plans, which include boosting internal controls, to Japan's Financial Services Agency.
The insurance policy mismanagement pushed corporate governance to the fore just as the government planned to sell $10 billion worth of shares in Japan Post Holdings to fund reconstruction in areas devastated by an earthquake and tsunami in 2011.
Masuda said the conglomerate expected to deal with 220,000 more cases of improper sales of its policies, affecting about 60,000 people.
Masuda, a former minister of Internal Affairs and Communications, took his post last month, succeeding Masatsugu Nagato, who resigned, along with heads of two Japan Post affiliates over the scandal.
By Junko Fujita