* Cyber attack raises uncertainty over impact on Japan companies
* Nomura Estate set to surge after source says Japan Post considers buying co
TOKYO, May 15 (Reuters) - Japanese stocks edged down on Monday morning, pressured by a stronger yen, a widespread cyber attack, and North Korea's missile test over the weekend.
The Nikkei share average fell 0.2 percent to 19,853.71 points in midmorning trade.
Officials across the globe scrambled to catch the culprits behind a massive ransomware worm that disrupted operations at car factories, hospitals, shops and schools.
Cyber security experts said the spread of the worm dubbed WannaCry - "ransomware" that locked up more than 200,000 computers in more than 150 countries - had slowed but that the respite might only be brief amid fears new versions of the worm will strike.
"We still don't know how much impact it has on Japanese companies. There is uncertainty looming, and when there is uncertainty, investors take profits," said Yoshihiro Okumura, general manager at Chibagin Asset Management.
The Nikkei has gained 9 percent since April 17, when it hit a five-month low of 18,224.68 points.
Sentiment also soured from a stronger yen. The yen rose against the dollar after U.S. data on Friday showed a smaller-than-expected increase in April retail sales, raising concerns about the retail sector and the broader economy.
Geopolitical tensions rose following a missile test by North Korea. Pyongyang said it had successfully conducted a newly developed mid-to-long range missile test, supervised by leader Kim Jong Un and aimed at verifying the capability to carry a "large scale heavy nuclear warhead," according to the North Korea's official KCNA news agency.
Exporters lost ground, with Toyota Motor Corp shedding 0.8 percent, Nissan Motor Co down 1.4 percent and Panasonic Corp 0.6 percent lower.
Elsewhere, Nomura Real Estate Holdings was untraded with a glut of buy orders after a source said on Saturday that Japan Post Holdings was considering buying the company in a bid to make real estate operations its new earnings pillar.
The broader Topix dropped 0.3 percent to 1,576.47 points, and the JPX-Nikkei Index 400 shed 0.2 percent to 14,080.66 points. (Editing by Randy Fabi)