An electromagnetic wave detector configured to detect electromagnetic waves by photoelectric conversion, the electromagnetic wave detector comprising: - a substrate; - an insulating layer provided on the substrate; - a graphene layer provided on the insulating layer; - a pair of electrodes provided on the insulating layer, each of the pair of electrodes being connected to the graphene layer; and - a contact layer provided so as to contact with the graphene layer, wherein the contact layer is made of a material having a polar group, and electric charges are formed in the graphene layer due to contact between the contact layer and the graphene layer, and characterized in that the contact layer is provided on the graphene layer, and another graphene layer is further provided so as to cover the contact layer and the graphene layer, and wherein the contact layer is sandwiched between the upper and lower graphene layers, and wherein a contact region and a non-contact region are respectively formed by the contact layer both in the upper graphene layer and in the lower graphene layer, forming an electron density gradient, and wherein photoelectric conversion is performed in both of the upper and lower graphene layers. electromagnetic waves by photoelectric conversion, the electromagnetic wave detector comprising: - a substrate; - an insulating layer provided on the substrate; - a graphene layer provided on the insulating layer; - a pair of electrodes provided on the insulating layer, each of the pair of electrodes being connected to the graphene layer; and - a contact layer provided so as to contact with the graphene layer, wherein the contact layer is made of a material having a polar group, and electric charges are formed in the graphene layer due to contact between the contact layer and the graphene layer, and characterized in that the contact layer is provided on the graphene layer, and another graphene layer is further provided so as to cover the contact layer and the graphene layer, and wherein the contact layer is sandwiched between the upper and lower graphene layers, and wherein a contact region and a non-contact region are respectively formed by the contact layer both in the upper graphene layer and in the lower graphene layer, forming an electron density gradient, and wherein photoelectric conversion is performed in both of the upper and lower graphene layers. - a substrate; - an insulating layer provided on the substrate; - a graphene layer provided on the insulating layer; - a pair of electrodes provided on the insulating layer, each of the pair of electrodes being connected to the graphene layer; and - a contact layer provided so as to contact with the graphene layer, wherein the contact layer is made of a material having a polar group, and electric charges are formed in the graphene layer due to contact between the contact layer and the graphene layer, and characterized in that the contact layer is provided on the graphene layer, and another graphene layer is further provided so as to cover the contact layer and the graphene layer, and wherein the contact layer is sandwiched between the upper and lower graphene layers, and wherein a contact region and a non-contact region are respectively formed by the contact layer both in the upper graphene layer and in the lower graphene layer, forming an electron density gradient, and wherein photoelectric conversion is performed in both of the upper and lower graphene layers. characterized in that the contact layer is provided on the graphene layer, and another graphene layer is further provided so as to cover the contact layer and the graphene layer, and wherein the contact layer is sandwiched between the upper and lower graphene layers, and wherein a contact region and a non-contact region are respectively formed by the contact layer both in the upper graphene layer and in the lower graphene layer, forming an electron density gradient, and wherein photoelectric conversion is performed in both of the upper and lower graphene layers.