A signal processing device includes a continuous film, a plurality of spin wave generators, and at least one signal detector. The continuous film includes at least one magnetic layer. The plurality of spin wave generators are provided on the continuous film in such a manner as to be in direct contact with the continuous film or be in contact with the continuous film while having an insulation layer interposed therebetween, and each has a contact surface with the continuous film in a dot shape and generates a spin wave in a region of the magnetic layer of the continuous film by receiving an input signal, the region being immediately under the contact surface. The signal detector is provided on the continuous film and detects, as an electrical signal, the spin waves generated by the spin wave generators and propagating through the continuous film.