A propylene elastomer (PBER) comprising (a) 50 to 85 mol % of units
derived from propylene, (b) 5 to 25 mol % of units derived from 1-butene
and (c) 10 to 25 mol % of units derived from ethylene, and having a molar
ratio of propylene content to ethylene content of from 89/11 to 70/30,
and a modulus in tension (YM), as measured in accordance with JIS 6301,
of not more than 40 Mpa.