A liquid medicine injection device (1) has an upper member (3), a lower member (2), and a sealing member (4) accommodated between both members. The lower member has a part (22a), for pressing a peripheral portion of the sealing member, which is formed of an upper surface of an annular wall part (22) and an annular edge part (25) formed at an inner side of the part (22a) for pressing the peripheral portion of the sealing member. An upper-surface side of a flange part (42) of the sealing member is pressed by the upper member, and an outer-edge portion of a lower-surface side of the flange part is pressed by the part (22a) for pressing the peripheral portion of the sealing member with the annular edge part (25) in penetration into an inner-edge portion of the lower-surface side of the flange part. As a result, there is a decrease of a skirt-shaped projected part (43) of the sealing member, and an outer peripheral surface of the lower end of a part (41b) to be inserted into the lower member closely contacts an inner surface of the annular wall part.
