First, wood or bamboo is crushed to obtain wood powder with an average grain size of 5 μm to 100 μm. Next, the wood powder is put in a first mold, and a first compression molding step is carried out under the conditions that, for example, a temperature is 160° C. and a pressure is 30 MPa. Thus, a temporary molded body is obtained. Subsequently, the temporary molded body is immersed in a flame retardant and a surface of the temporary molded body is impregnated with the flame retardant. Thereafter, the temporary molded body is put in a second mold, and a second compression molding step is carried out under the conditions that, for example, a temperature is 200° C. and a pressure is 100 MPa. At this time, ingredients such as lignin and a hemicellulose are separated from the wood powder, and function as an adhesive. For this reason, pieces of crushed material are firmly bonded with each other so as to be integrated into a single body. Thus, a compression-molded product with a predetermined shape is obtained.