A thermal radiation light source configured to receive heat as an input and to generate electromagnetic waves as an output, comprising: a) a laminated body (10S; 10SB) including m quantum well structure layers (111, 112; 111B, 112B, 113B) that are laminated, that each have a quantum well structure, and that have different magnitudes of transition energy between subbands respectively, and including an n-layer (121, 122; 121B, 122B) and a p-layer (13; 131B, 132B) sandwiching each of the quantum well structure layers (111, 112; 111B, 112B, 113B) from both sides in the laminating direction wherein the n-layer (121, 122; 121B, 122B) is made of an n-type semiconductor and the p-layer (13; 131B, 132B) is made of a p-type semiconductor; b) a voltage applying unit (151, 152; 151A, 151B; 152A, 152B) that is provided for each of the m quantum well structure layers (111, 112; 111B, 112B, 113B) and is directly or indirectly connected to the n-layer (121, 122; 121B, 122B) and the p-layer (131B, 132B) sandwiching each quantum well structure layer (111, 112; 111B, 112B, 113B) and that is configured to apply a voltage for moving a charge in a quantum well of each quantum well structure layer (111, 112; 111B, 112B, 113B) to the n-layers (121, 122; 121B, 122B) or the p-layer (13; 131B, 132B); c) a voltage switching unit (17, 161, 162; 161A, 161B; 162A, 162B) that is configured to switch ON/OFF of application of the voltage to each of the m quantum well structure layers (111, 112; 111B, 112B, 113B); and d) a photonic crystal portion (20; 20B; 20C; 20D) disposed in the laminated body (10S; 10SB) or adjacent to the laminated body (10S; 10SB), and including a periodic refractive index distribution having a single period so that lights of a total of m kinds of wavelengths resonate, each of the lights of the m wavelengths being generated in each of the m quantum well structure layers (111, 112; 111B, 112B, 113B) corresponding to transition energy between subbands in the quantum well of the quantum well structure layer (111, 112; 111B, 112B, 113B); characterized in that the m is 2 and in that the 2 kinds of wavelengths are a resonance wavelength of a fundamental mode and a resonance wavelength of the first higher-order mode of the photonic crystal portion (20; 20B; 20C; 20D). a) a laminated body (10S; 10SB) including m quantum well structure layers (111, 112; 111B, 112B, 113B) that are laminated, that each have a quantum well structure, and that have different magnitudes of transition energy between subbands respectively, and including an n-layer (121, 122; 121B, 122B) and a p-layer (13; 131B, 132B) sandwiching each of the quantum well structure layers (111, 112; 111B, 112B, 113B) from both sides in the laminating direction wherein the n-layer (121, 122; 121B, 122B) is made of an n-type semiconductor and the p-layer (13; 131B, 132B) is made of a p-type semiconductor; b) a voltage applying unit (151, 152; 151A, 151B; 152A, 152B) that is provided for each of the m quantum well structure layers (111, 112; 111B, 112B, 113B) and is directly or indirectly connected to the n-layer (121, 122; 121B, 122B) and the p-layer (131B, 132B) sandwiching each quantum well structure layer (111, 112; 111B, 112B, 113B) and that is configured to apply a voltage for moving a charge in a quantum well of each quantum well structure layer (111, 112; 111B, 112B, 113B) to the n-layers (121, 122; 121B, 122B) or the p-layer (13; 131B, 132B); c) a voltage switching unit (17, 161, 162; 161A, 161B; 162A, 162B) that is configured to switch ON/OFF of application of the voltage to each of the m quantum well structure layers (111, 112; 111B, 112B, 113B); and d) a photonic crystal portion (20; 20B; 20C; 20D) disposed in the laminated body (10S; 10SB) or adjacent to the laminated body (10S; 10SB), and including a periodic refractive index distribution having a single period so that lights of a total of m kinds of wavelengths resonate, each of the lights of the m wavelengths being generated in each of the m quantum well structure layers (111, 112; 111B, 112B, 113B) corresponding to transition energy between subbands in the quantum well of the quantum well structure layer (111, 112; 111B, 112B, 113B);