Obverse

Cherry blossoms, authority abve, value below

Lettering: 日 本 国 百 円

Translation: 
State of Japan 100 yen

Reverse

Large value in center, date below

Lettering: 100  昭和55年

Translation: Year 55 of Shōwa

Edge: Reeded

Just about all modern Japanese coins are really cool. Their designs are artistic and very interesting. Flowers are a recurring theme. These are cherry blossoms.
The date of these coins is keyed to the start of the reigning dynasty. Arabic numerals on the '100' side give the years elapsed since the beginning of the dynasty, either Showa (emperor Hirohito) or Akihito (emperor Heisei). You can figure the Gregorian date on these coins by adding a start date to the numeral shown. For numerals greater than 41, add 1925 (start of the Showa dynasty). For numerals less than 41, add 1988 (start of the Akihito dynasty). For instance, if the numerals are 55, the Gregorian year is 1925 + 55 = 1980AD; if the numerals are 12, the Gregorian year is 1988 + 12 = 2000AD.
These coins are made of copper nickel and are worth face value (100 yen in Japan).