A liquid medicine injection device has an upper member, a lower member, and a sealing member between both members. The lower member has a part, for pressing a peripheral portion of the sealing member, formed of an upper surface of an annular wall part and an annular edge part at an inner side of the part for pressing the peripheral portion of the sealing member. An upper-surface side of a flange part 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 for pressing the peripheral portion with the annular edge part in penetration into an inner-edge portion of the lower-surface side of the flange part. An outer peripheral surface of the lower end of a part to be inserted into the lower member contacts an inner surface of the annular wall part.
