To prevent liquid leakage from the tips of pipettes, when the pipettes are extracted from a channel.

Two nozzles 60 are formed in a pipet head 51. A pipet tip 50 is inserted in each nozzle 60 to constitute two pipettes 19a and 19b. Pumps 52 are each connected to the pipettes 19a and 19b, and each pump 52 is independently driven by a pump driver 53 and a controller 55 to make each of the pipettes 19a and 19b draw liquid by suction and discharge it. When the pipettes 19a and 19b are each extracted from the channel 16, a weak suction force is provided for each of the pipettes 19a and 19b by each pump 52. Liquid leakage from their tips is prevented by the suction force.