By pushing down a shutter release operation member (9), that is mounted on a front of a waterproof case of a waterproof type lens-fitted photo film unit, a release lever (70) is caused to rotate through a rotary shaft (71) that is put through a front wall of the waterproof case. Thereby, the release lever directly pushes an arresting member (59) through an opening (19c) provided on a front side of a unit body (3), releasing a shutter drive member (51) as having been arrested in a cocked position by the arresting member (59), and thus causing a shutter blade (45) to make an open-close movement. The waterproof case consists of a pair of case members that are put on the unit body from its front and rear sides, and are joined to each other by engagement. An elastic waterproof ring is force-fitted in a gap of the joint between the case members. The waterproof ring has a substantially semicircular sectional contour, and is provided with a ridge on a flat surface portion on the opposite side from a curved surface portion.