Hitachi Construction Machinery Co., the world's biggest maker of giant excavators, has offered 689 million Australian dollars ($529 million) to buy Australia's Bradken Ltd. The purchase would be its biggest ever and is likely to boost profit by about 10 percent, Nomura Securities Co. said.

The Tokyo-based company said Monday it is offering AU$3.25 a share.

The acquisition will enable Hitachi Construction to supplement its parts business for mining equipment and boost earnings, according to a statement. The announcement comes about two months after its larger domestic rival, Komatsu Ltd., agreed to buy U.S.-based Joy Global Inc. for $2.89 billion, signaling the company's optimism that demand for diggers and loaders will rebound after years of declining commodity prices.