A variable-rigidity device includes a tubular member including a plurality of high-rigidity portions and low-rigidity portions arranged along a longitudinal axis, a core member arranged on an inner side of the tubular member and including a plurality of high-rigidity core portions and low-rigidity core portions; and an actuator configured to relatively move the core member with respect to the tubular member, in which the actuator is configured to cause a first force to repeatedly fluctuate with a passage of time, the first force causing the core member to relatively move with respect to the tubular member in an axial direction along the longitudinal axis.