Toyota may be riding high when it come to sales in the U.S., but the automaker's CEO sees a lot of trouble on the horizon.

Akio Toyoda cites an appreciating yen, the European debt crisis and prospects of slowing automobile demand in the U.S. as top concerns for Japan's automobile industry, Bloomberg News reports.

"In the short run, the European economy and a possible slowdown in the recovery of the U.S. auto market is a concern," Bloomberg News quotes Toyoda as saying in remarks as chairman of the Japan Automobile Manufacturers Association. The yen is also a "major concern," he said.

For the moment, he isn't writing off 2012. Lots of people have cars that are wearing out, and they need to replace them. Around the world, Toyota sees its overall sales growing 21% this month.

"In Europe, where vehicle ownership is already very high, the cycle that drivers replace their old cars may slow down, but measures to avoid a major slowdown in the replacement cycle are taken in each country," Toyoda said. "In emerging markets, demand itself is growing, so volume itself will still grow."

His remarks come just as Toyota reported terrific May sales increases -- up 87% from the same month a year ago. But overall U.S. vehicle sales slowed a bit from their torrid pace at the start of the year.

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