A fund backed by Japan's most prominent activist investor said Tuesday it is launching a takeover bid of up to ¥25.9 billion for Toshiba Machine Co., even though the former Toshiba Corp. unit has threatened to implement defense measures.

Hostile bids are rare in Japan but have been increasing as the government promotes corporate governance reform to make management more accountable to investors.

City Index Eleventh Co., backed by veteran activist investor Yoshiaki Murakami, said it will offer ¥3,456 per Toshiba Machine share to buy up to 43.82 percent of the molding machine company, spending up to ¥25.9 billion.