The present invention achieves an electronic pen capable of flexibly changing the mode of use of a side switch function, in accordance with a need of a user. A side switch unit (3) has an engagement portion (31FT) at one end in an axial direction, and a pressed portion (31BK) at another end. One end side of the side switch unit (3) is obliquely inserted to butt against one end side of a side-surface opening (11H) of a case (11), and another end side is pushed down toward the side-surface opening (11H). The engagement portion (31FT) engages with the case (11), and the pressed portion (31BK) is pressed toward the one end side by a pressing mechanism portion (70), and thereby the side switch unit (3) is attached to the side-surface opening (11H) portion of the case (11).