An insertion device is used to deform a deformable intraocular lens to a reduced size and insert the deformed lens into an eye through an insertion tube. The insertion device includes a push rod for pushing and inserting the lens into the eye, and a posture control member disengagably engaged with a tip end portion of the push rod. The posture control member prevents deflection of the push rod from a center axis. The engagement between the posture control member and the push rod is broken when the push rod arrives at a predetermined position during a step of advancing the push rod.