A liquid medicine self-administration device including a flexible reservoir, an operating member, a pushing member to move with respect to the operating member and to induce pressure deformation of the reservoir, and engaging means engages the operating member. With the operating member engaged by the engaging means, the pushing member is relatively moved to the operating member based on restoring force of a spring member to push the reservoir by the pushing member. By disengaging means moving in unison with the pushing member, the engaging means is released from an engaged state with respect to the operating member, when the pushing member has moved to a predetermined location while pushing the reservoir.