Binder and formed body producing method

A formed body producing method comprising:

• an accumulating step of accumulating a mixture including cellulose fibers and a binder, the binder including
• starch particle configured to mutually bind the cellulose fibers when water is provided, and
• inorganic oxide particles, wherein
• the binder includes a composite particle in which the starch particle and the inorganic oxide particles are integrated such that the inorganic oxide particles are attached to the surface of the starch particle before the accumulating step,
• the inorganic oxide particles contain carbon, and
• the content of the carbon is 2% by mass or more relative to the mass of the inorganic oxide particles;
• a humidifying step of providing the accumulated mixture with water to facilitate a hydrogen bond between the cellulose fibers and the starch particle of the binder;
• and
• a forming step of obtaining a formed body by heating and applying pressure to the mixture provided with water.