A deflection device includes a tabular object for transmitting or reflecting an electromagnetic wave, a drive unit for driving the tabular object so as to rotate or perform a translation motion, and an electromagnetic wave irradiation unit for irradiating the tabular object with an electromagnetic wave so that an irradiation area extending in a direction intersecting a direction of the rotation or translation motion of the tabular object is formed. The deflection device is characterized in that, in order to change a direction of transmission or reflection of an electromagnetic wave radiated on the irradiation area by the rotation or translation motion of the tabular object, a plurality of grooves extending in an in-plane direction of the tabular object is provided in a section of the tabular object along a longitudinal direction of the irradiation area, and the plurality of grooves is formed so that intervals of the plurality of grooves which passes through the irradiation area are changed by the rotation or translation motion of the tabular object.