According to an embodiment, a determination device includes a first calculator, a second calculator, a determination unit, and an output unit. The first calculator is configured to calculate inclination information that indicates inclination of an attachment surface to which a body unit is to be attached, based on acceleration of the body unit measured during a first period. The second calculator is configured to calculate difference information that indicates a difference between the inclination information stored in a storage and inclination information newly calculated by the first calculator. The determination unit is configured to determine that an attached state of the body unit with respect to the attachment surface changes when the difference information continuously indicates a difference not less than a predetermined value during a second period. The output unit is configured to output information based on a determination result obtained by the determination unit.
