A key cylinder for an electronic locking device including: a cylinder housing forming an appearance, and a cylinder plug positioned in an axis direction in the cylinder housing, rotatably installed in place and locking and releasing the cylinder housing, wherein the cylinder plug includes a lock head including a key insertion hole into which a key head of an electronic key is removably insertable to a front side, a printed circuit board exchanging power and authentication data from the publicly known electronic key by installing key connection pins (12, 13 and 14) in a connection housing installed through the lock head, accessing to the key connection pins (12, 13 and 14) and equipped with a microprocessor and EEPROM, a driving motor performing normal rotation and reverse rotation drive in accordance with an input signal of the printed circuit board, a spur gear installed in an axis of the driving motor, a lock pin guider fixed in a rear direction of the cylinder plug, a direction conversion rotary ring rotating in accordance with drive of the driving motor by an internal gear, the direction conversion rotary ring being rotatably installed through a fixing axis in the center of the lock pin guider and the internal gear being engaged with the spur gear formed in the direction conversion rotary ring in a front direction and a spiral groove formed in the direction conversion rotary ring in a rear direction, and a lock pin installed in the lock pin guider such that the lock pin fluctuates within a pin hole formed in a direction perpendicular to an axis direction of the cylinder plug, a foot pin of the lock pin inserted into one side of a spiral groove formed in the direction conversion rotary ring, positioned through a straight guide wall intercommunicating with the pin hole, and appearing and disappearing in lock holes (51 and 52) formed in the cylinder housing by moving in a perpendicular direction to axis rotation of the direction conversion rotary ring through installation of the foot pin in the spiral groove, the foot pin performing straight line motion to realized locking and release of the key cylinder. a cylinder housing forming an appearance, and a cylinder plug positioned in an axis direction in the cylinder housing, rotatably installed in place and locking and releasing the cylinder housing, wherein the cylinder plug includes a lock head including a key insertion hole into which a key head of an electronic key is removably insertable to a front side, a printed circuit board exchanging power and authentication data from the publicly known electronic key by installing key connection pins (12, 13 and 14) in a connection housing installed through the lock head, accessing to the key connection pins (12, 13 and 14) and equipped with a microprocessor and EEPROM, a driving motor performing normal rotation and reverse rotation drive in accordance with an input signal of the printed circuit board, a spur gear installed in an axis of the driving motor, a lock pin guider fixed in a rear direction of the cylinder plug, a direction conversion rotary ring rotating in accordance with drive of the driving motor by an internal gear, the direction conversion rotary ring being rotatably installed through a fixing axis in the center of the lock pin guider and the internal gear being engaged with the spur gear formed in the direction conversion rotary ring in a front direction and a spiral groove formed in the direction conversion rotary ring in a rear direction, and a lock pin installed in the lock pin guider such that the lock pin fluctuates within a pin hole formed in a direction perpendicular to an axis direction of the cylinder plug, a foot pin of the lock pin inserted into one side of a spiral groove formed in the direction conversion rotary ring, positioned through a straight guide wall intercommunicating with the pin hole, and appearing and disappearing in lock holes (51 and 52) formed in the cylinder housing by moving in a perpendicular direction to axis rotation of the direction conversion rotary ring through installation of the foot pin in the spiral groove, the foot pin performing straight line motion to realized locking and release of the key cylinder.