An abnormality determining apparatus includes an information storing device that stores information, an information obtaining device that obtains information of a detection subject, a receiving device that receives abnormality presence/absence information indicative of the presence or absence of an abnormality in the detection subject detected by a user, a normal group data set constructing device that constructs a normal group data set that is a collection of normal data indicating that the detection subject is in a normal state based on the abnormality presence/absence information received by the receiving device and based on the information obtained by the information obtaining device during a preset period, and a determining device that determines the presence or absence of an abnormality in the detection subject by performing calculations based on the normal group data set stored in the information storing device and based on the information obtained by the information obtaining device.