After a morning of debate, a special house committee gave the green light to the bill, which would give Tokyo far broader powers in deciding what constitutes a state secret, and severely punish those who leak the information.
"It is an urgent task to prepare for legislation that should remain secret at a time when fears over information leaks are growing," Prime Minister Shinzo Abe told the committee.
"Frankly speaking, there is misunderstanding," Abe said. "I want to firmly say that it is obvious that normal reporting activity of journalists must not be a subject for punishment under the bill."
Local media said the committee, dominated by his ruling coalition, was always likely to give the nod to the legislation, clearing the way for a vote in the full chamber later in the day.
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Abe's ruling coalition, which controls both the lower and upper houses, aims to enact the bill by December 6 when the current parliament session ends, despite growing concerns among major opposition parties and the public.
Under the proposals, information related to defence, diplomacy, counter-intelligence and counter-terrorism can all be classified as a state secret, at the behest of politicians.
Critics argue that the bill could mean far more information being kept from the public, with little real oversight.
The legislation is aimed at plugging Japan's notoriously leaky bureaucracy after years of complaints from chief ally the United States, which has been reluctant to pool information.