Most of low speeds rotating machines are large and important equipments in plants, and the stoppage caused by damage of rolling element bearing brings serious losses. This paper relates to a diagnosis bearing in low speed rotating equipment of 100 rpm or less, and proposes a method using AE envelope waveform of a 100 k to 1 MHz frequency region. Abnormality diagnosis was enabled even from rotation of 1 rpm by improving the S/N ratio by the method of further amplifying after envelope processing in addition to amplification of AE waveform. Furthermore, a method to remove electric noises in an event counting method and an abnormality judgment method by an event counting method in low speed rotation are proposed. The proposed methods are applied to implement a diagnostic instrument and are actually utilized for the abnormality diagnosis and condition monitoring on sites, which shows the validity of the proposal.