Abstract: The device uses the principle of the Doppler effect laser velocimeter. It comprises emitter and receiver optic guides formed by integrated optics techniques on a single substrate, preferably made of glass. The emitter guides, connected to a light source, produce two mutually coherent beams inclined with respect to one another in such a way as to constitute interference fringes in a measuring volume situated outside the substrate. The receiver guides transmit the light diffused by the passage of particles in movement through the measuring volume to a detection and processing circuit. The substrate is mounted in a support fixed in an orifice of a wall along which a fluid flows transporting the particles to be examined. The substrate comprises a face which comes into contact with the fluid. This device enables the velocity, size and/or number of particles in movement in a fluid moving along a wall to be determined.