PURPOSE: To provide a method to measure conveniently on-line the coffee liquid concentration extracted from the coffee bean powder by the hot water and an automatic vending machine of coffee equipped with such a measuring method.

CONSTITUTION: At a hot water tube 9 to supply hot water 9a to a coffee extracting device 4 to extract the coffee liquid from a coffee bean powder 2a to the hot water 9a, and respective tube paths of a coffee liquid tube 10 to transfer an extracted coffee liquid 4a, flow-through type electrical conductivity measuring instruments 17 and 18 are provided. The electrical conductivity of the coffee liquid 4a is the measured value to which an inorganic ion component and an organic ion component are related, and therefore, by obtaining the value, the concentration of the coffee liquid 4a can be quantitatively obtained on-line. At the coffee automatic vending machine, the obtained electrical conductivity measured result is outputted through a computing element to a concentration display.