The man in Chiba, in suburban Tokyo, was hurt in the eye by a broken screw last July, the Japanese industry ministry said.
“The cause of the accident is believed to be the customer using an inappropriate size of straight slot driver instead of a cross slot,” the ministry said in a recent report.
“But the instructions on the product failed to give enough information on what kind of screwdriver should be employed or to alert customers on the risk of building the product,” it said.
Ikea has won legions of fans with its affordable yet stylish designs, but its no-frills self-assembly approach has also caused legendary tales of frustration.
Ikea, which re-entered the Japanese market in 2006, said it believed its instructions were already detailed.
“It was the first and only accident reported,” Ikea Japan spokeswoman Yuki Kusama said on Monday.
“But we were told by the ministry to provide more comprehensible instructions,” she said.
The company now sets out written instructions in Japanese after earlier relying mostly on illustrations, she said.
Ikea arrived in Japan in 1974 but was forced to withdraw after failing to win over the country’s notoriously finicky consumers.
The Swedish giant competes here against against well-known retailers such as Muji, the “no brand” Japanese homeware outlet which has become increasingly popular overseas.