An electrolytic test machine includes an electrolytic cell in which an electrolytic liquid is stored so that a test material is immersed in the electrolytic liquid. An electrode is immersed in the electrolytic liquid. A DC power source supplies a current between the test material and the electrode. A treating pipe line extends from the electrolytic cell to collect a harmful gas which is generated from the electrolytic liquid during supplying of a current and which is released out of the electrolytic liquid, along with the electrolytic liquid. A harmful gas purifying device is disposed in the treating pipe line. The harmful gas purifying device includes a catalyst for purifying the harmful gas, and a determining device for determining the replacement time of the catalyst.