PURPOSE: To obtain a drip condition sensor being workable for a long time by detecting vibration produced in a liq. drop cylinder caused by dropping and feeding of liq. drops into the liq. drop cylinder, detecting existence of the liq. drops based on a vibration detecting signal from a vibration detecting device by means of a signal treating circuit part and judgeing drip-advancing condition.

CONSTITUTION: Liq. drops 6 falls on and collides with the wall face of a liq. drop cylinder 5 or a liq. reservoir 7 of the lower part of the liq. drop cylinder to produce vibration. A vibration-detecting device 1 is tightly fixed on the outer wall face of the liq. drop cylinder 5 by means of a fixture 2 to detect vibration caused by fall and collision of the liq. drops 6. A signal treating circuit part 3 judges drip-advancing condition by detecting existence of falling liq. drops 6 based on the vibration detecting signal of the vibration detecting device 1. In addition, for detecting vibration, as vibration caused by falling and collision of the liq. drops is transmitted to the whole wall face of the liq. drop cylinder 5, whereever the vibration detecting device 1, namely fixture 2 is set on the liq. drop cylinder 5, falling of the liq. drops 6 can be detected surely. It is obtain thereby a drip condition sensor being workable for a long time without being influenced by setting position and setting environment.