To realize a concrete form, which has a simple structure, is lightweight and has a favorable operativity by a method wherein an inner form is made of one tube, both end parts of which are supported by inserting holes formed on an outer form and by expanding which the shape of the inner form is formed and by contracting which can be put in and pulled out of the outer form through the inserting holes.

After an outer form 5 is assembled, an inner form, which is made of a tube 6 or a tube 6 and a steel plate 7 wound on the outer periphery of the tube 6, is inserted through an inserting hole 13 provided on an outer form 15 and set to the outer form 5. Under the state just mentioned above, the air is inserted in the tube 6 so as to expand the whole inner form. In this state, a ready-mixed concrete is charged between the outer form 5 and the inner form and then solidified. When a solidifying process completes, the air in the tube 6 is extracted so as to contract the tube 6. By making the diameter of the tube 6 smaller by means of an external force caused by pulling out the inner form through the inserting hole 13 of the outer form 5, the whole inner form is pulled out through the inserting hole 13 of the outer form 5. After the inner form is pulled out, a concrete product in the outer form 5 is removed from the outer form 5.