Cylinder lock

A cylinder lock comprising:

• a rotor with a circular cross-sectional shape having a key insertion hole at its central part, the rotor being rotatably fitted into a fixed cylinder body and including
• tumbler insertion holes arranged on opposite sides or one side of one diametric line of the rotor and each having opposite ends opened to an outer surface of the rotor, the tumbler insertion holes being provided in a plurality of positions at intervals in an axial direction of the rotor while intersecting with part of the key insertion hole within planes orthogonal to an axis of the rotor;
• a plurality of half tumblers each having an engagement portion on one of opposite end portions along the one diametric line, the half tumblers being respectively inserted into the tumbler insertion holes in such a manner as to be movable between engagement positions to cause the engagement portions to protrude from the outer surface of the rotor and disengagement positions to retract the engagement portions back into the tumbler insertion holes in response to insertion of a legitimate mechanical key into the key insertion hole;
• springs respectively provided between the half tumblers and the rotor and configured to bias the half tumblers toward the engagement positions;
• and
• locking recesses extending in the axial direction of the rotor and being provided in inner surfaces of an upper side wall and a lower side wall of the cylinder body such that the engagement portions of the half tumblers located in the engagement positions are capable of being inserted into and engaged with the locking recesses,
• wherein
• inner side surfaces of each of the tumbler insertion holes facing the corresponding half tumbler from opposite sides are each formed to include at least:
• a guide portion closely facing the half tumbler and extending in a moving direction of the half tumbler;
• and
• a passage forming portion having larger clearance between the passage forming portion and the half tumbler than clearance between the guide portion and the half tumbler in such a manner as to form a release passage between the passage forming portion and the half tumbler such that the release passage crosses a side edge portion of the key insertion hole, extends in the moving direction of the half tumbler, and has opposite ends opened to the outer surface of the rotor.