A liquid detector includes: a case; a sensor base; a sensor chip; and a partition wall, dividing a part of a flow channel in the case into an upstream and downstream buffer chambers. The sensor chip includes a sensor cavity adapted to receive a liquid to be detected. The sensor base has: a first hole through which the liquid is introduced from the upstream buffer chamber to the sensor cavity; and a second hole through which the liquid is introduced from the sensor cavity to the downstream buffer chamber. The first and second holes are arranged in parallel at the same height, the partition wall is arranged between the first and second holes so as to extend along the sensor base, and a bottom bypass is formed at a lowermost position of the upstream and downstream buffer chambers to communicate the upstream and downstream buffer chambers with each other.