An acoustic emission measuring device in which a piezoelectric element (63) used as an AE sensor is secured to the inner ring (62) of a ball bearing (61) fixedly fitted onto a rotating shaft (60). The axial end face of a roughly tire-shaped case (65), which is capable of rotating in synchronism with the inner ring (62) and storing a first coil in which a current flows from the piezoelectric element (63), is secured to the inner ring (62). The axial end face of a roughly tire-shaped case (66) for storing a second coil is secured to an outer ring (64). The first coil and the second coil are oppositely disposed radially outside of the rotating shaft (60) so that the first coil and the second coil can face each other in the radial direction.