PURPOSE: To prevent breakage of an oil than and avoid mixing of air into oil by projectingly providing a pair of engine suspension brackets in front of the crankshaft of a crankcase, and arranging the oil pan between the engine suspension brackets.

CONSTITUTION: The crankcase 11 of a unit swing type engine 4 loaded on a scooter type motorcycle is constituted by joining an L side and an R side crankcase elements 21, 22 together. In this case, engine suspension brackets 23 are respectively projectingly provided on the lower part in front of respective crankcase elements 21, 22 and in front of the crankshaft 11A, and these suspension brackets 23 are journaled on a body frame 24. On the lower part in front of the crankcase, an oil pan 26 is arranged between a pair of the suspension brackets 23. The upper part outer wall of the oil pan 26 functions as a part of seal of the fitting seat face of the forced air cooling cover of the engine, and forced cooling air flowing in the forced air cooling cover blows against the outer wall of the oil pan 26.