An extravasation detecting apparatus is provided which is capable of detecting at an early stage the dislodgment of a tip opening of a solution supplying tool from a blood vessel. The extravasation detecting apparatus includes: a fluid delivery unit which supplies a fluid medicine by repetitively performing operations of pressing and occluding a portion between a fluid medicine containing unit and a puncture site of an infusion tube, subsequently suctioning the fluid medicine from upstream using a restoring force of the infusion tube, and once again pressing and occluding the infusion tube to push out the fluid medicine toward downstream; a tube closing unit located upstream of the fluid delivery unit; and a blood detecting sensor which operates the tube closing unit during a solution supplying operation to generate negative pressure in a downstream infusion tube and which detects whether or not blood is being suctioned between the fluid delivery unit and the puncture site into the infusion tube from a punctured blood vessel.