An infusion pump for delivering drug to a patient by causing a distal opening portion of an endovascular indwelling catheter or an indwelling needle, which communicates with an infusion tube, to indwell inside a vein or an intestinal tract of the patient, the pump comprising: a drive motor; a liquid delivering drive unit that delivers the drug inside the infusion tube by pressing the infusion tube on account of a rotor of the drive motor in forward rotation; a rotational direction detection device that generates detection information regarding a rotational direction for judging whether the rotor of the drive motor is in the forward rotation or reverse rotation; and a control unit; characterized in that the rotational direction detection device comprising: an encoder plate having an inner circumferential region of a light blocking pattern portion and an outer circumferential region of the light blocking pattern portion, and an optical coupler having a light emitting unit and a light receiving unit used for generating the detection information; wherein the control unit judges whether the rotor of the drive motor is in the forward rotation or the reverse rotation based on the detection information regarding the rotational direction obtained from the rotational direction detection device, using detection information of the inner circumferential region and the outer circumferential region, wherein the judging is based on comparison of current information with information stored in a judging table; and the control unit also judges whether or not a rotational speed of the rotor is normal, based on the information in the judging table. a drive motor; a liquid delivering drive unit that delivers the drug inside the infusion tube by pressing the infusion tube on account of a rotor of the drive motor in forward rotation; a rotational direction detection device that generates detection information regarding a rotational direction for judging whether the rotor of the drive motor is in the forward rotation or reverse rotation; and a control unit; characterized in that the rotational direction detection device comprising: an encoder plate having an inner circumferential region of a light blocking pattern portion and an outer circumferential region of the light blocking pattern portion, and an optical coupler having a light emitting unit and a light receiving unit used for generating the detection information; wherein the control unit judges whether the rotor of the drive motor is in the forward rotation or the reverse rotation based on the detection information regarding the rotational direction obtained from the rotational direction detection device, using detection information of the inner circumferential region and the outer circumferential region, wherein the judging is based on comparison of current information with information stored in a judging table; and the control unit also judges whether or not a rotational speed of the rotor is normal, based on the information in the judging table. an encoder plate having an inner circumferential region of a light blocking pattern portion and an outer circumferential region of the light blocking pattern portion, and an optical coupler having a light emitting unit and a light receiving unit used for generating the detection information; wherein the control unit judges whether the rotor of the drive motor is in the forward rotation or the reverse rotation based on the detection information regarding the rotational direction obtained from the rotational direction detection device, using detection information of the inner circumferential region and the outer circumferential region, wherein the judging is based on comparison of current information with information stored in a judging table; and the control unit also judges whether or not a rotational speed of the rotor is normal, based on the information in the judging table.