To provide a convertible penetration opening form formed in a synthetic resin tube and removable from a solidified concrete without damage by folding to the inside in the axial direction.

This convertible beam penetration opening form includes two synthetic resin tubular forms fitted to each other while leaving the slight gap therebetween. The two tubular forms are provided to the penetration opening form at the beam part of a reinforced concrete structure. Several grooves are formed in the inner surfaces of the tubular bodies in the axial direction. Since the thickness of the groove part is as thin as 0.5-1.2 mm, the groove part is easily deformed when an external force is applied thereto. Consequently, the form can be easily removed without damage from the solidified concrete by bending to the inside and thereby can be converted.