An abnormality detection apparatus (2000) handles tasks allocated to a plurality of processing servers (3200) as processing targets in a distribution system (3000) having the processing servers (3200). A history acquisition unit (2020) acquires progress history information which is information regarding progress of the plurality of tasks at a plurality of time point of recording. A target range determination unit (2040) determines a target range. A distribution calculation unit (2060) calculates a task speed distribution which is a probability distribution of processing speeds of the tasks using the progress history information regarding the plurality of tasks. An abnormality determination unit (2080) compares a processing speed of a task to be determined with the task speed distribution to thereby determine whether or not the processing speed of the task to be determined is abnormal.