To correctly adjust the amount of one drop of liquid and surely drop one drop of liquid by setting a branch pipe having an air reservoir at a buret and switching a two-way valve thereby dropping the liquid drop by a pressure of the air reservoir.

A two-way valve (e) is registered with a position where a buret pipe (a) upper than a branching start end of a branch pipe (d) communicates with the branch pipe (d). As a result, a liquid in the pipe (a) is supplied to an air reservoir (c) via the branch pipe (d) owing to a pressure difference between liquid levels in the pipe (a) and air reservoir (c). At this time, the air in the air reservoir (c) is compressed thereby to balance the pressure difference of the liquid levels in the pipe (a) and air reservoir (c), so that a fixed amount of the liquid is supplied. Thereafter, the two-way valve (e) is turned 90° in the counterclockwise direction. Since the branch pipe (d) is communicated with a buret pipe (b) lower than the branching start end of the branch pipe (d), the liquid is discharged until the air reservoir (c) is turned to a normal pressure. When the fixed amount of the liquid is discharged and the pressure in the air reservoir (c) is balanced with the atmospheric pressure, the liquid is not discharged any more.