The apparatus developed in our department for electrocochleography is described. The principle of enhancement of a weak biological signal from background noise by an average response computer is elucidated, with indication of the limitations. The frequency content of the effective tone-burst sound stimulus was calculated to estimate the frequency specificity of the stimulus. A description is also given of the signal switching circuitry used to make separate recordings of CM and AP simultaneously. Some details are given of a circuit permitting rapid determination of AP threshold values and input-output curves with tone-bursts. Because the apparatus was developed to be applicable for experimental work and for auditory evoked response audiometry, several special features were incorporated. A circuit for accurate measurement of latency, a double-synchronized tone-burst generator, and a dB-linear intensity ramp with I’M bursts are briefly described. A flexible trigger generator provides many trigger modes for single tone-burst and pulse-train stimulation. These stimuli can be used with various interstimulus and interseries intervals. Continuous and forward-masking experiments with tones or noises can be performed. The tone-burst shape can be varied within wide limits.