The box-shaped robot is only 5 millimetres (0.2 inch) long, 9 millimetres (0.36 inch) wide and 6.5 millimetres (0.26 inch) high. It has a pair of round connectors on both sides that can be linked up with other robots for more extensive assignments.
With a weight of only 0.42 grams (0.0147 ounces), the robot can lift objects twice as heavy as itself and can move at a speed of 2 millimetres (0.1 inch) per second, said Koji Hirose, spokesman for the Ministry of International Trade and Industry.
Mitsubishi Electric Corp., Sumitomo Electric Industries Ltd. and Matsushita Research Institute Tokyo, Inc. developed the machine under the government's 25 billion yen (£126m) ``micro machine'' project that began in 1989, Hirose said.
The robots are one of three types of machines designed for use in different environments, he said.
The robots, which can crawl into the tiniest gaps around bundles of pipes, are expected to speed up inspection and repairs at electric and nuclear power plants because they can be sent in while the plants keep running.
Scientists are working to add new functions to them so the robots can climb up and down a pipe while connected to other machines. They also plan to develop robots with motors and problem-detecting sensors.