An electromagnetic wave detector for converting an electromagnetic wave into an electric signal and detecting the electric signal, comprising: - a substrate; - an insulating layer provided on the substrate, p-type and n-type graphene layers (1, 2) juxtaposed on the insulating layer; a first electrode and a second electrode (3, 4) disposed facing each other with the p-type and n-type graphene layers (1, 2) interposed, the first electrode being one electrode electrically connected to both the p-type and n-type graphene layers (1, 2) at one ends, the second electrode being two electrodes electrically connected to other ends of the p-type and n-type graphene layers (1, 2), respectively; a gate electrode (21, 23) that applies an operation voltage to the p-type and n-type graphene layers (1, 2); a balance circuit connected between the two second electrodes; and a detection circuit that detects electric signal between the two second electrodes, wherein the p-type graphene layer has a Dirac point voltage higher than the operation voltage, and the n-type graphene layer has a Dirac point voltage lower than the operation voltage, in a state in which an electromagnetic wave is not incident on the p-type and n-type graphene layers (1, 2), the balance circuit makes the first electrode and the second electrode (3, 4) have an identical potential, in a state in which the electromagnetic wave is incident on the p-type and n-type graphene layers (1, 2), the Dirac point voltages of the p-type graphene layer and n-type graphene layer shift, the detection circuit detects an electric signal between the second electrodes, and the electric signal in the state in which the electromagnetic wave is incident is output. - a substrate; - an insulating layer provided on the substrate, p-type and n-type graphene layers (1, 2) juxtaposed on the insulating layer; a first electrode and a second electrode (3, 4) disposed facing each other with the p-type and n-type graphene layers (1, 2) interposed, the first electrode being one electrode electrically connected to both the p-type and n-type graphene layers (1, 2) at one ends, the second electrode being two electrodes electrically connected to other ends of the p-type and n-type graphene layers (1, 2), respectively; a gate electrode (21, 23) that applies an operation voltage to the p-type and n-type graphene layers (1, 2); a balance circuit connected between the two second electrodes; and a detection circuit that detects electric signal between the two second electrodes, wherein the p-type graphene layer has a Dirac point voltage higher than the operation voltage, and the n-type graphene layer has a Dirac point voltage lower than the operation voltage, in a state in which an electromagnetic wave is not incident on the p-type and n-type graphene layers (1, 2), the balance circuit makes the first electrode and the second electrode (3, 4) have an identical potential, in a state in which the electromagnetic wave is incident on the p-type and n-type graphene layers (1, 2), the Dirac point voltages of the p-type graphene layer and n-type graphene layer shift, the detection circuit detects an electric signal between the second electrodes, and the electric signal in the state in which the electromagnetic wave is incident is output. p-type and n-type graphene layers (1, 2) juxtaposed on the insulating layer; a first electrode and a second electrode (3, 4) disposed facing each other with the p-type and n-type graphene layers (1, 2) interposed, the first electrode being one electrode electrically connected to both the p-type and n-type graphene layers (1, 2) at one ends, the second electrode being two electrodes electrically connected to other ends of the p-type and n-type graphene layers (1, 2), respectively; a gate electrode (21, 23) that applies an operation voltage to the p-type and n-type graphene layers (1, 2); a balance circuit connected between the two second electrodes; and a detection circuit that detects electric signal between the two second electrodes, wherein the p-type graphene layer has a Dirac point voltage higher than the operation voltage, and the n-type graphene layer has a Dirac point voltage lower than the operation voltage, in a state in which an electromagnetic wave is not incident on the p-type and n-type graphene layers (1, 2), the balance circuit makes the first electrode and the second electrode (3, 4) have an identical potential, in a state in which the electromagnetic wave is incident on the p-type and n-type graphene layers (1, 2), the Dirac point voltages of the p-type graphene layer and n-type graphene layer shift, the detection circuit detects an electric signal between the second electrodes, and the electric signal in the state in which the electromagnetic wave is incident is output.