The invention concerns a turntable-using testing apparatus suitable for use in carrying out performance test of, for example, an internal combustion engine. The apparatus has testing units radially arranged on a turntable, each testing unit having a computer, table-side connectors connected to individual computers, a transfer device provided outside the turntable for delivering an object to be tested onto and withdrawing same from one of the testing units, and ground-side connectors connectable to and disconnectable from the table-side connectors and connected to the host computer. The apparatus enables prompt transmission/reception of test data and the like, facilitates correction of troubles and/or failures, and permits mass signal transmission and reception. According to another aspect of the invention, each of the testing units arranged on the turntable has a testing device, a control section, and a display, so that test data received from the testing device into the control section can, in combination with decision data thereof, be displayed on the display unit.