An interchangeable cylinder lock core with a mechanism for transferring a torque to a lock unit when a key plug is rotated. The interchangeable cylinder lock core includes a shell having an upper part, provided with a central row of locking pins in associated cavities, and a lower part with a cylindrical bore accommodating the rotatable key plug. At least a part of the cylindrical bore extends through a rotatable retainer sleeve. A back region of the key plug has a minimum length with the adjoining front region of the key plug being located in front of the mechanism for transferring torque. The adjoining front region accommodates, in addition to the central row of locking pins, at least one side locking mechanism which is located in its entirety within the front region of the key plug and interacts with at least one recess in a fixed front end sleeve portion.