A continuous microorganism cultivating apparatus has a stock solution tank which receives a stock solution for a microbial reaction and is provided with a cylindrical filter through which the stock solution is passed. The stock solution is separated by the filter into filtrate containing a metabolic product and concentrated liquid containing microbes. The concentrated liquid is then recycled to the stock solution. The filter is a ceramic filter having a multitude of pores, which is connected to a back wash device.
