To provide a rotation speed detection device which is improved to manage a sensor and a sensor target integrally, to prevent both the sensor and a pulser ring from being contaminated by water and the like, and to reduce the sizes of a crystal gap and an air gap compared with the conventional device, and also to provide a rolling bearing device using the rotation speed detection device.

The sensor and a sensor target, in other words, a magnetized body 67 is arranged in a space 90 waterproofed by a fixing side core metal 21, a slinger 33, and an elastic sealing member 65.