PURPOSE: To adopt a propulsive device equipped to a portable boat in accordance with a type of the boat, by removably mounting a propulsive unit through a combining means to a body of the rearmost part of the boat consisting of a main unit, connecting unit and float units.

CONSTITUTION: A main unit A and connecting unit B are butted with each of their end face and connected by screwing of bolts 30 and nuts 31. Then float units C are connected to both sides of the units A and B by screwing of bolts 30 and nuts 31 to assemble a boat. A propulsive unit D is connected to a rear end of the unit A, and the rearmost part of this boat, by screwing of bolts 30 and nuts 31 to form the boat with a propulsive device. To disassemble this boat, the bolts 30 and the nuts 31 are untightened to remove the unit D, house the unit B in the unit A and accommodate the units C in said unit B thus the boat can be compactly formed and carried.