The Nikkei 225 index lost 182.95 points to 14,880.82 at the start.
Market participants are also waiting for the outcome of a Bank of Japan policy meeting concluding Tuesday, he told Dow Jones Newswires.
Data from the US Labor Department on Friday showed jobs growth plodded along at a solid but unspectacular pace in March as the economy appeared to be emerging from one of the coldest winters in recent memory.
The world's largest economy added 192,000 jobs in March -- a shade below analysts' average estimate of 195,000 net new jobs -- and the unemployment rate held steady at 6.7 per cent.
The dollar dropped on Friday as the jobs report suggested the Federal Reserve is unlikely to hasten its timetable for tightening monetary policy.
The greenback was at 103.29 yen early Monday, hardly changed from 103.26 yen in New York Friday afternoon but well below 103.88 yen in Tokyo earlier Friday before the US data came out.
The euro bought 141.48 yen, against 141.50 yen in New York on Friday and 142.36 yen in Tokyo earlier Friday.
A strong yen is negative for Japanese exporters as it makes them less competitive abroad and erodes repatriated profits.