Abstract: A joining device includes a male member having a shaft portion, and a tubular female member having a mating portion whereto the shaft portion is inserted and fitted, which are capable of detachably joined with each other. The shaft portion includes, on an outer surface thereof and along an axial line direction, a plurality of protruded portions about an axial line of the shaft portion in a cross section taken along an axial line direction and protruded over an entire perimeter. The mating portion includes, on an inner surface thereof and along an axial line direction, a plurality of recessed portions about an axial line of the mating portion in a cross section taken along an axial line direction and recessed over an entire perimeter. The shaft portion and the mating portion are joined by being engaged at the protruded portions and the recessed portions.