A coil bobbin includes: a body portion around which a coil is wound and having a cylindrical shape; a pair of flange portions formed at both ends of the body portion respectively; and terminal portions which are formed in the pair of flange portions, respectively, the terminal portions being around which respective ends of the coil are wound. The pair of flange portions have thicker portions and thinner portions, respectively, different from each other in thickness. The pair of flange portions is formed to gradually reduce a thickness from the thicker portions toward the thinner portions, respectively. The terminal portions are formed in the thicker portions, respectively.