To provide a recording medium cutting device capable of detecting the sharpness of a cutting blade, and grasping the change timing of the cutting blade.

The recording medium cutting device having a cutting blade 5 to cut a recording medium P and cutting the recording medium by moving the cutting blade 5 in the width direction of the recording medium P has a detection means 8 to detect that side parts Pa and Pb are inclined along the moving direction of the cutting blade 5 when the cutting blade 5 is moved to a vicinity of the side parts Pa and Pb of the recording medium P and in a vicinity of the cutting position by the cutting blade 5, and brought into contact with one side part Pa (Pb) of the recording medium P.