An infusion pump comprising: a tube installation unit in which an infusion tube allowing a drug in a drug containing bag to be infused into a patient is installed in use in a lateral horizontal direction; and a delivery driving unit that, with the infusion tube installed in the lateral horizontal direction, applies peristaltic motion to the infusion tube to deliver the drug in a delivery direction preset along the lateral horizontal direction, the tube installation unit comprising: a bubble detecting sensor that detects a bubble generated in the infusion tube; characterised in that the tube installation unit further comprises: a downstream occlusion sensor that detects a blocked state of the infusion tube; and a control unit that determines that the infusion tube is set in a direction opposite to the delivery direction based on a value of a downstream occlusion signal with a tendency toward an increase from the downstream occlusion sensor obtained when, with the infusion tube set in the direction opposite to the delivery direction, a clamp for the infusion tube between the drug containing bag and the delivery driving unit is opened by the control unit to carry out priming, instead of driving the delivery driving unit, for filling the drug from the drug containing bag into the infusion tube to deliver the drug to the patient, the downstream occlusion signal indicating that an internal pressure of the infusion tube has increased. a tube installation unit in which an infusion tube allowing a drug in a drug containing bag to be infused into a patient is installed in use in a lateral horizontal direction; and a delivery driving unit that, with the infusion tube installed in the lateral horizontal direction, applies peristaltic motion to the infusion tube to deliver the drug in a delivery direction preset along the lateral horizontal direction, the tube installation unit comprising: a bubble detecting sensor that detects a bubble generated in the infusion tube; characterised in that the tube installation unit further comprises: a downstream occlusion sensor that detects a blocked state of the infusion tube; and a control unit that determines that the infusion tube is set in a direction opposite to the delivery direction based on a value of a downstream occlusion signal with a tendency toward an increase from the downstream occlusion sensor obtained when, with the infusion tube set in the direction opposite to the delivery direction, a clamp for the infusion tube between the drug containing bag and the delivery driving unit is opened by the control unit to carry out priming, instead of driving the delivery driving unit, for filling the drug from the drug containing bag into the infusion tube to deliver the drug to the patient, the downstream occlusion signal indicating that an internal pressure of the infusion tube has increased. a bubble detecting sensor that detects a bubble generated in the infusion tube; characterised in that the tube installation unit further comprises: a downstream occlusion sensor that detects a blocked state of the infusion tube; and a control unit that determines that the infusion tube is set in a direction opposite to the delivery direction based on a value of a downstream occlusion signal with a tendency toward an increase from the downstream occlusion sensor obtained when, with the infusion tube set in the direction opposite to the delivery direction, a clamp for the infusion tube between the drug containing bag and the delivery driving unit is opened by the control unit to carry out priming, instead of driving the delivery driving unit, for filling the drug from the drug containing bag into the infusion tube to deliver the drug to the patient, the downstream occlusion signal indicating that an internal pressure of the infusion tube has increased. a downstream occlusion sensor that detects a blocked state of the infusion tube; and a control unit that determines that the infusion tube is set in a direction opposite to the delivery direction based on a value of a downstream occlusion signal with a tendency toward an increase from the downstream occlusion sensor obtained when, with the infusion tube set in the direction opposite to the delivery direction, a clamp for the infusion tube between the drug containing bag and the delivery driving unit is opened by the control unit to carry out priming, instead of driving the delivery driving unit, for filling the drug from the drug containing bag into the infusion tube to deliver the drug to the patient, the downstream occlusion signal indicating that an internal pressure of the infusion tube has increased.