TOKYO, Feb 5 - Japan will tell fellow Group of Seven members when they meet later this week that it will take firm action in the currency market when exchange rate moves are very speculative, Vice Finance Minister Masakazu Hayashi said on Thursday. "Sudden moves in exchange rates are undesirable," he added at a regular news conference. Finance ministers and central bankers from G7 leading economies are due to meet in Boca Raton, Florida on Friday and Saturday.//