An electronic pen comprising an electronic pen cartridge (3, 3A, 3AS) and an electronic pen casing (2, 2C, 2D, 2E, 2F, 2G, 2H), wherein the electronic pen cartridge (3, 3A, 3AS) is housed in a hollow part (2a, 2Ca,2Da, 2Ea, 2Fa, 2Ga, 2Ha) of the electronic pen casing (2, 2C, 2D, 2E, 2F, 2G, 2H) in which an opening is made on a pen tip side that is one end side in an axis center direction, the electronic pen cartridge (3, 3A, 3AS) including: a pen tip part that is capable of protruding to the external through the opening, a first electronic circuit including a circuit configured to couple with a position detecting sensor, a rear-end-part connector that is disposed at the rear end part of the electronic pen cartridge on the opposite side to the pen tip part in the axis center direction, wherein the rear-end-part connector includes plural terminal parts (31a, 31b, 32a, 32b, 33a, 33b, 34a, 34b, 35a, 35b) that are each electrically connected to the first electronic circuit and are insulated from each other; and the electronic pen casing (2, 2C, 2D, 2E, 2F, 2G, 2H) including: a connector for joining disposed on a rear end side of the hollow part of the electronic pen casing, wherein the connector for joining (13J, 17J, 2CJ, 2DJ, 2EJ) includes plural terminal parts (31a, 31b, 32a, 32b, 33a, 33b, 34a, 34b, 35a, 35b) insulated from each other, a second electronic circuit electrically connected to the plural terminal parts of the connector for joining (13J, 17J, 2CJ, 2DJ, 2EJ), and a power supply that provides a supply voltage to the second electronic circuit; wherein the rear-end-part-connector joins the connector for joining (13J, 17J, 2CJ, 2DJ, 2EJ), and wherein the rear-end-part connector and the connector for joining (13J, 17J, 2CJ, 2DJ, 2EJ) are joined through insertion of a fitting protrusion of one of the rear-end-part connector and the connector for joining (13J, 17J, 2CJ, 2DJ, 2EJ) into a fitting recess of the other in the axis center direction and the plural terminal parts (31a, 31b, 32a, 32b, 33a, 33b, 34a, 34b, 35a, 35b) are formed to have circular annular conductor contact parts in either of the rear-end-part connector and the connector for joining. a pen tip part that is capable of protruding to the external through the opening, a first electronic circuit including a circuit configured to couple with a position detecting sensor, a rear-end-part connector that is disposed at the rear end part of the electronic pen cartridge on the opposite side to the pen tip part in the axis center direction, wherein the rear-end-part connector includes plural terminal parts (31a, 31b, 32a, 32b, 33a, 33b, 34a, 34b, 35a, 35b) that are each electrically connected to the first electronic circuit and are insulated from each other; and the electronic pen casing (2, 2C, 2D, 2E, 2F, 2G, 2H) including: a connector for joining disposed on a rear end side of the hollow part of the electronic pen casing, wherein the connector for joining (13J, 17J, 2CJ, 2DJ, 2EJ) includes plural terminal parts (31a, 31b, 32a, 32b, 33a, 33b, 34a, 34b, 35a, 35b) insulated from each other, a second electronic circuit electrically connected to the plural terminal parts of the connector for joining (13J, 17J, 2CJ, 2DJ, 2EJ), and a power supply that provides a supply voltage to the second electronic circuit; wherein the rear-end-part-connector joins the connector for joining (13J, 17J, 2CJ, 2DJ, 2EJ), and wherein the rear-end-part connector and the connector for joining (13J, 17J, 2CJ, 2DJ, 2EJ) are joined through insertion of a fitting protrusion of one of the rear-end-part connector and the connector for joining (13J, 17J, 2CJ, 2DJ, 2EJ) into a fitting recess of the other in the axis center direction and the plural terminal parts (31a, 31b, 32a, 32b, 33a, 33b, 34a, 34b, 35a, 35b) are formed to have circular annular conductor contact parts in either of the rear-end-part connector and the connector for joining. the electronic pen casing (2, 2C, 2D, 2E, 2F, 2G, 2H) including: a connector for joining disposed on a rear end side of the hollow part of the electronic pen casing, wherein the connector for joining (13J, 17J, 2CJ, 2DJ, 2EJ) includes plural terminal parts (31a, 31b, 32a, 32b, 33a, 33b, 34a, 34b, 35a, 35b) insulated from each other, a second electronic circuit electrically connected to the plural terminal parts of the connector for joining (13J, 17J, 2CJ, 2DJ, 2EJ), and a power supply that provides a supply voltage to the second electronic circuit; a connector for joining disposed on a rear end side of the hollow part of the electronic pen casing, wherein the connector for joining (13J, 17J, 2CJ, 2DJ, 2EJ) includes plural terminal parts (31a, 31b, 32a, 32b, 33a, 33b, 34a, 34b, 35a, 35b) insulated from each other, a second electronic circuit electrically connected to the plural terminal parts of the connector for joining (13J, 17J, 2CJ, 2DJ, 2EJ), and a power supply that provides a supply voltage to the second electronic circuit; wherein the rear-end-part-connector joins the connector for joining (13J, 17J, 2CJ, 2DJ, 2EJ), and wherein the rear-end-part connector and the connector for joining (13J, 17J, 2CJ, 2DJ, 2EJ) are joined through insertion of a fitting protrusion of one of the rear-end-part connector and the connector for joining (13J, 17J, 2CJ, 2DJ, 2EJ) into a fitting recess of the other in the axis center direction and the plural terminal parts (31a, 31b, 32a, 32b, 33a, 33b, 34a, 34b, 35a, 35b) are formed to have circular annular conductor contact parts in either of the rear-end-part connector and the connector for joining.