A bicycle electric power source assembly comprises a tubular member, an electric power source member and a restricting member. The tubular member includes an inner peripheral surface, an outer peripheral surface and a through hole that passes through the tubular member between the inner peripheral surface and the outer peripheral surface. The electric power source member is disposed inside the tubular member. The electric power source member includes a restriction accepting part. The restricting member is disposed in the through hole. The restricting member includes a restricting part that engages with the restriction accepting part to restrict relative movement of the electric power source member with respect to the tubular member in an axial direction of the tabular member.