A detection device includes a processing device and a storage medium. An ideal waveform signal indicating an ideal waveform of a servo pattern signal which is a result of reading a servo pattern recorded in a servo band of a magnetic tape by a servo reading element is stored in advance in the storage medium. The processing device acquires a servo band signal which is a result of reading the servo band by the servo reading element, and detects the servo pattern signal by comparing the servo band signal with the ideal waveform signal.