TOKYO, May 23 (Reuters) - Japan's factory activity crept into expansion for the first time in a year in May, a business survey showed on Thursday, as manufacturing gathered pace after months of weakness.

The au Jibun Bank flash Japan manufacturing purchasing managers' index (PMI) climbed to 50.5 in May from 49.6 in April, breaching the 50.0 threshold separating growth from contraction last seen in May last year.

"The expansion in business activity remained services-led, but the near-stabilisation of manufacturing output offers hope of growth broadening out later in the year," said Jingyi Pan, economics associate director at S&P Global Market Intelligence, which compiled the survey.

Both output and new orders, the two key subindexes contributing to the headline figure, contracted at a slower pace, while stocks of purchases rose at the fastest pace in 10 months.

Manufacturers' optimism, though, dipped and inflationary pressures pushed up input costs and output prices.

Japan's business-to-business wholesale inflation held steady at 0.9% in April as the yen's declines pushed up import costs, government data showed last week, with analysts expecting it to accelerate in coming months.

Meanwhile, the service sector kept expanding in May but at a slower pace as new business growth slowed down.

The au Jibun Bank flash services PMI dropped to 53.6 in May from April's final reading at 54.3.

Still, strong business confidence prodded employment levels to increase at a quicker pace, according to the survey.

Both average input costs and output prices rose at a slower pace, but inflation hovered well above their respective long-run averages.

The au Jibun Bank flash Japan composite PMI, which combines both manufacturing and service sector activity, went up slightly to 52.4 in May from 52.3 in April, the highest since last August. (Reporting by Satoshi Sugiyama. Editing by Sam Holmes)