There is no set rule or shared agreement among G7 advanced nations on what kind of currency moves are defined as "excess volatility" that justify intervention, Shinohara said.
"But usually, when you talk about excess volatility you have in mind a timeframe of several days or weeks," rather than several months, he said in an interview on Friday.
The remarks contrast with those of incumbent top currency diplomat Masato Kanda, who said on Wednesday that steady yen falls over a protracted period could also warrant intervention.
G7 and G20 major economies have a shared understanding that currency moves ought to reflect economic fundamentals, and that excess volatility was undesirable.
In Japan, the finance ministry has jurisdiction over currency policy and decides whether and when to intervene.
Persons:
Kim Kyung, Naoyuki Shinohara, Shinohara, Masato Kanda, Leika Kihara, Kim Coghill
Organizations:
National Printing Bureau, Bank of Japan, REUTERS, Reuters, International Monetary Fund, Thomson
Locations:
Tokyo, Japan, TOKYO, Asia