To provide a cylinder lock for a building, which can effectively prevent picking thereof.

The cylinder lock for the building consists of a holder 1 mounted in a door main body for the building, with an engaging groove formed in the internal peripheral surface thereof, and a cylinder main body 11 rotatably arranged in the holder 1. The cylinder main body 11 is comprised of a plurality of tumblers 15, and a side bar 20 arranged therein. The tumblers 15 are energized in a direction orthogonal to an insertion direction of a key 31, and upon insertion of the key 31, notches 17 formed in respective side edges of the tumblers are aligned. The side bar 20 is energized toward the tumblers 15, and before insertion of the key 31, it abuts on the side edges of the respective tumblers 15 to protrude from the cylinder main body 1, to thereby engage with the engaging groove of the holder 1. On the other hand, by engaging with the notches 17 aligned upon insertion of the key 31, the side bar 20 sinks into the cylinder main body 11. According to the cylinder lock thus formed, a protective member 34 formed of a hard metallic material is arranged on the outside of the side bar 20.