An industrially advantageous process for producing adamantane by which high-purity adamantane reduced in coloration is efficiently produced while minimizing the loss. The process, which is for producing adamantane by isomerizing trimethylenenorbornane, includes (A) a reaction step of isomerizing the starting material, (B) a concentration step of concentrating the adamantane contained in the resultant liquid reaction mixture, (C) a crystallization step of precipitating the concentrated adamantane, (D) a solid-liquid separation step of separating the adamantane crystals from the slurry resulting from the crystallization, (E) a washing step of washing the isolated adamantane crystals, and (F) a drying step of drying the adamantane crystals washed, characterized in that the mass ratio of the endo-trimethylenenorbornane to the adamantane each contained in the materials to be subjected to the crystallization step (C) (endo-trimethylenenorbornane/adamantane) is 0.25 or lower.