To continue rotation of an engine even if any fault is generated especially in a battery in a ship body side by providing with an engine operation continuation compensation means for reducing an engine operation continuation inhabitation factor by the engine operation parts of a ship body side, in a small boat in which an outboard motor is mounted on a stern.

Power from two couples of batteries 16a, 16b mounted in a ship body is supplied to an engine control system through a main switch and a diode by a feed circuit 17b. An a.c. generator 21 and both batteries 16a, 16b are connected to each other through charging circuit 30, in which both ends of the coil 21a of a generator 21 and one battery 16a are connected to each other through diodes 22a, 22b, 23a, 23b by the charging circuit 17a, and also both ends of the coil 21a and the other battery 16b are connected to each other through diodes 27a, 27b, 23a, 23b by a charging circuit 17a'. It is thus possible to continue engine operation even if any fault is generated in a connecting condition on one battery side.