"The state funeral ceremony is imposed by the decision of the Cabinet of Ministers. Naturally, this causes rejection and doubts for many people," the head of the party, Kenta Izumi, was quoted as saying by the news agency.
Japan's Communist Party, the left-wing party Reiwa Shinsengumi and the Democratic Party have also announced earlier that they would boycott Abe's state funeral.
The opposition parties in Japan sharply criticize the decision of the current government to hold a state funeral ceremony for Abe, the costs of which will be fully covered from the state budget, without proper discussions in parliament. The decision on the state funeral was made by the Cabinet of Ministers. This decision is also not supported by more than half of the Japanese.
The ceremony will take place in Tokyo on September 27.
Abe was attacked on July 8 in the Japanese city of Nara during a campaign speech. His killer, Tetsuya Yamagami, approached the politician from behind and fired two shots from a distance of about 10 meters (33 feet). Police said Abe was conscious immediately after being wounded, but then, during transportation to a hospital, his condition became critical with cardiac and pulmonary arrest. Later in the day, the Nara Medical University hospital pronounced him dead. Abe was 67. His funeral and cremation took place on July 12.
Abe's state funeral will be the second state funeral held in Japan for a former prime minister since World War II. The first one was held in 1967 for Shigeru Yoshida. Over 6,000 Japanese and foreign officials are expected to attend Abe's funeral.