Isuzu Motors Ltd. said Thursday its group net profit plunged 27.4 percent to 26.02 billion yen in the six months to Sept. 30, mainly due to an increase in research and development spending by the truck maker.

In its earnings report for the first half of fiscal 2005, Isuzu Motors, an affiliate of General Motors Corp., said its operating profit shrank 12.9 percent to 37.87 billion yen and its pretax profit dropped 15.9 percent to 40.62 billion yen.

But sales at the company for the six-month period, whose main business is truck and diesel engine manufacturing, rose 0.3 percent to 737.33 billion yen.

Isuzu said it is planning to double its full-year dividend for the business year to next March 31 to 3 yen from 1.5 yen for the previous business year. The company also said it would pay an interim dividend, as it did last year.

Isuzu said the number of vehicles sold on the domestic market rose 8.1 percent to 46,236 in the wake of stricter government regulations on emissions of nitrogen oxides and particulates.

The tougher environmental rules have encouraged truck users to replace their existing fleets with new models with advanced emissions-control equipment.

For the full year to next March, the company forecasts a group net profit of 55 billion yen, while pretax profit is expected to reach 90 billion yen on projected sales of 1.58 trillion yen.

In fiscal 2004, Isuzu Motors posted all-time highs of 60.04 billion yen for net profit, 87.21 billion yen for operating profit and 91.56 billion yen for pretax profit.