The paper describes an automatic test apparatus designed to check, under mass-production conditions and within broad limits of impedance, the multiple circuit paths found in modern radio equipment. While primarily intended as a check of wiring, the instrument operates by comparing with a standard the circuit impedances from point to point, and supersedes the common ohmmeter by working successively on alternating and direct current to provide a degree of discrimination between the reactive and resistive elements of a complex network. The comparison method used in the design provides the necessary flexibility for adaptation to differing production requirements, and it has been found that the apparatus gives a consistently greater degree of reliability in circuit checking than has been attained by purely manual operation.