Operability, accuracy, and safety when fitting a glass-made pipette tip to a pipette are improved. A pipette tip fitting adapter includes a hollow body having one end portion configured to serve as a tip inserting portion into which a pipette tip is inserted, and the other end portion configured to serve as a pipette inserting portion into which a pipette is inserted, and at an opening side of an inner circumferential surface of the tip inserting portion, seal portions projecting inward are formed in a circumferential direction. Accordingly, a pipette tip that is long and heavy like a glass tip can be held.