Problems to be solved: Providing a structure for connection and separation between an engine and a main unit, adapted to release coupling by separating a centrifugal clutch.Means for solving the problems: A structure for connection and separation includes an engine side adapter (1) with a clutch shoe (11), an engine side annular surface (121), and an engine side projection (13); and a main unit side adapter (2) with a clutch drum (21), a main unit side annular surface (221), and a main unit side projection (23), wherein the engine side projection (13) projects in a radial direction from a circle centered on the power transmission shaft as a center, and the main unit side projection (23) projects in a direction radially opposite to the direction in which the engine side projection (13) projects; and when the engine side adapter (1) or the main unit side adapter (2) is relatively rotated about the axis of the power transmission shaft with the engine side annular surface (121) and the main unit side annular surface (221) brought into contact with each other, the engine side projection (13) and the main unit side projection (23) are moved to a back side of each other from the circumferential direction to be engaged in the axial direction of the power transmission shaft.