Abstract: Apparatus for testing metal detecting apparatus employs a test piece of representative metal which is passed through a section of the electromagnetic field of the metal detecting apparatus to record a response signal as if metal has been detected. The testing apparatus comprises the test piece and a housing for the test piece which extends through said section of the electromagnetic field and acts to guide the test piece along its path, said movement of the test piece causing distortion of the electromagnetic field and actuation of the detecting mechanism to give the required signal. Metal detecting apparatus may have the testing apparatus attached thereto or moulded integrally therewith.