To always safely fasten and hold a sensor with a sensor holder by making use of a fastening force of an attaching band without using a setscrew for fixing the sensor to the sensor holder regardless of the direction of a slit of the sensor holder.

In this sensor holding device for the cylinder, a detection switch 3 for detecting position of a piston is inserted and fixed in a sleeve-like switch holder 8 having a slit 7, the sensor holder 8 is fitted inside of a grasping part 11 of an attaching band 16 wound on the outer periphery of a cylinder body 5, and is pressed from the upper side with the grasping part 11 and fixed to the outer periphery of the cylinder body 5. A chevron-shaped top part 8b is formed in the sensor holder 8, thereby clearance between the attaching band and a corner part of the grasping part 11 is created.