An apparatus for testing a defect, includes a semiconductor element. In the semiconductor element, a conductive film is formed on an STI (shallow trench isolation) insulating film, which fills a shallow trench extending into a semiconductor region, opposing said semiconductor region through an insulating film in an ordinary state, and the shallow trench is not completely or sufficiently filled with the STI insulating film in a defective state. Also, the apparatus includes a control circuit configured to set a test mode in response to a test mode designation signal, a first voltage applying circuit configured to output a first voltage to the conductive film in the test mode, and a second voltage applying circuit configured to output a second voltage to the semiconductor region in the test mode. The first voltage is higher than the second voltage, and a voltage difference between the first voltage and the second voltage is sufficient to cause breakdown between the conductive film and the semiconductor region in the defective state.