To effectively utilize scrap gypsum molded products such as waste gypsum boards, and in more detail to effectively utilize the scrap gypsum molded products by obtaining gypsum hardened products containing a porous adsorbent having a harmful gas-adsorbing function and a humidity-adjusting function.

This gypsum hardened products containing the porous adsorbent features that the scrap gypsum molded products are heated under atmospheric pressure or pressurization at 60-230°C to obtain regenerated hemihydrate gypsum and the regenerated hemihydrate gypsum is mixed with the porous adsorbent comprising at least one kind selected from the group consisting of diatomaceous soil, activated carbon, charcoal, crystalline silicic acid, noncrystalline silicic acid, aluminum silicate, hardened matter obtained by acidifying the incinerated ash of sewage sludge, activated soil, acid white clay and zeolite, followed by being hardened.