A pipette with an adjustable volume of an aspirated liquid built of a handle and of a nozzle and of coupled with them an exchangeable pipette tip ejection mechanism comprising an ejector push button seated in the upper part of said handle and an ejector seated with its lower end onto said nozzle, a drawing up and discharging mechanism comprising a pipetting push button connected via a pipetting rod with a piston assembly of which a plunger is placed in said nozzle, a plunger working stroke adjustment mechanism provided with a drive assembly of an adjustment screw of a plunger working stroke with at least one driving member, a manually actuated lock mechanism locking said plunger working stroke adjustment mechanism, an engaging mechanism engaging said plunger working stroke adjustment mechanism with a counter for indicating a volume of a liquid aspirated by said pipette depending on the set plunger working stroke, a calibration mechanism for a change of a pipette calibration coefficient determining a relationship between a plunger movement length which is set by said plunger working stroke adjustment mechanism and the liquid volume indicated in said counter, whereas said driving member of said drive assembly of said adjustment screw of the plunger working stroke is accessible from outside through at least one window in a wall of said handle, characterised in that said lock mechanism locking said plunger working stroke adjustment mechanism comprises a lock member which is non-rotatably mounted relative to said pipette handle and is axially slidable between LOCKED POSITION and UNLOCKED POSITION of said plunger working stroke adjustment mechanism, whereas said driving member of said drive assembly of said adjustment screw of the plunger working stroke is axially fixedly and rotatably mounted relative to said pipette handle, and said lock mechanism locking said plunger working stroke adjustment mechanism constitutes a friction brake between said lock member and said driving member, whereas said lock member has a frictional surface on an inner cone and said driving member has a frictional surface on an outer cone. an exchangeable pipette tip ejection mechanism comprising an ejector push button seated in the upper part of said handle and an ejector seated with its lower end onto said nozzle, a drawing up and discharging mechanism comprising a pipetting push button connected via a pipetting rod with a piston assembly of which a plunger is placed in said nozzle, a plunger working stroke adjustment mechanism provided with a drive assembly of an adjustment screw of a plunger working stroke with at least one driving member, a manually actuated lock mechanism locking said plunger working stroke adjustment mechanism, an engaging mechanism engaging said plunger working stroke adjustment mechanism with a counter for indicating a volume of a liquid aspirated by said pipette depending on the set plunger working stroke, a calibration mechanism for a change of a pipette calibration coefficient determining a relationship between a plunger movement length which is set by said plunger working stroke adjustment mechanism and the liquid volume indicated in said counter, whereas said driving member of said drive assembly of said adjustment screw of the plunger working stroke is accessible from outside through at least one window in a wall of said handle,