A liquid medicine administration device (10) is provided with a barrel (12), a gasket (22), and a plunger mechanism (14A) . The plunger mechanism (14A) is provided with a rotary member (30), a first moving member (31), and a second moving member (32). An extension operation of the plunger mechanism (14A) has a first extension operation and a second extension operation. In the first extension operation, the first moving member (31) advances to a predetermined position with respect to the rotary member (30) and the second moving member (32) in conjunction with rotation of the rotary member (30). In the second extension operation, the second moving member (32) advances with respect to the rotary member (30) together with the first moving member (31) after the first extension operation, in conjunction with rotation of the rotary member (30).
