Balancer device of an engine, engine provided therewith and method of assembling a balancer device to an engine

A first balancer shaft (11) includes a shaft extension portion (26) extending forward, to which a driven sprocket (16) is attached. A case member (13) includes a first bearing portion (31; 32, 33) supporting the balancer shaft (11) near its weight portions (21, 22) and rotational gear (23), and a second bearing portion (34) supporting the same near its driven sprocket (16). The case member (13) includes an upper case (13U) coupled to a cylinder block (4) and a lower case (13L) facing to the upper case (13U), and there is provided a case extension portion (41) extending forward at the upper case (13U). The first bearing portion (31; 32, 33) is configured of a hole formed by half-split portions of the both cases (13U, 13L), and the second bearing portion (34) is configured of a hole formed integrally at the case extension portion (41).