Abstract: Provided are a stock solution concentrating device, a stock solution treatment device and a circulation-type treatment device that can prevent the deposition of cells and the like on a filtration member and that can continuously filter and concentrate a stock solution such as pleural and ascitic fluid or blood plasma. The stock solution concentrating device concentrates a stock solution such as pleural and ascitic fluid or blood plasma to form a concentrated solution, and is equipped with: a filter (10) having a filtration member that filters the stock solution; a concentrator (20) to which the filtrate which has been filtered is supplied, and which concentrates the filtrate to form a concentrated solution; and a stock solution supply unit that supplies the stock solution to the filter (10). The stock solution supply unit has a supply amount adjustment function for adjusting the amount of the stock solution supplied to the filter.