PURPOSE: To enable detecting of the presence or absence of leaking water irrespectively of the position where the water leaks by detecting the intervals of the water drops discharged in the terminal part of a flow passage system of a flow analyzing device.

CONSTITUTION: A flow injection analysis device measures the change in color by bringing a sample 5 and a reagent 1 into reaction. The reagent 1 is fed by a liquid feed pump 2 and the sample 5 is metered at a specified rate by a sampling valve 3 and is mixed with the reagent 1. The liquid mixture passes a reaction vessel 7 kept at a constant temp. and flows to a flow cell 9 in a colorimeter 8. The liquid is thereafter discharged in the form of water drops 19 from a drain D. A capillary nozzle 18 detects the water drops by means of a photointerruptor 20 provided in the drain D. The photointerruptor 20 consists of an LED and a phototransistor and detects the intervals of the water drops by means of a microcomputer 15. The leaking water is thus detected irrespectively of the position where the water leaks.