PURPOSE: To connect with an electrode electrically without requiring slide system connecting parts, and to execute a test with high accuracy, fixing an electrode supporting body, mounting a drip-feed device on a rotary table, and making it execute a drop-feed by intermittent motion.

CONSTITUTION: On the upper surface of a fixed table 16 are arrayed 12 pieces of electrode supporting bodies 2 at equal intervals in the shape of a circle. A drip-feed device 5 which is mounted onto a rotary table 10 is equipped with a vessel 17 containing a testing liquid, a drop-feed pump 18, a supporting body 20 for supporting a drip-feed nozzle 4 which is connected with the pump with a flexible pipe 19, a support 21 which is interlocked with the rotary table and moves the supporting body 20 up and down, a cam plate 22, and a roller 23, and drips a testing liquid between the opposed electrodes. According to such a constitution, when supplying the electric power between the opposed electrodes and detecting a leakage current, it is unnecessary to install a slide system conductive mechanism, therefore, there is no inconvenience that causes minute electric discharge which cannot be separated from a small tracking phenomenon.