An infrared sensor comprising: a base substrate; a bolometer infrared receiver; a first beam; and a second beam, wherein each of the first beam and the second beam has a connection portion (16A, 16B) connected to the base substrate and/or a member on the base substrate and a separated portion away from the base substrate, and is physically joined to the infrared receiver at the separated portion, the infrared receiver is supported by the first beam and the second beam to be away from the base substrate, the infrared receiver includes a resistance change portion including a resistance change material an electrical resistance of which changes with temperature, the resistance change portion includes an amorphous semiconductor, and each of the first beam and the second beam includes a crystalline semiconductor made of a base material same as a base material of the resistance change material, and is electrically connected to the resistance change portion at the separated portion, characterized in that a section of the first beam, the section being between a portion joined to the infrared receiver and the connection portion, has a first phononic crystal structure having a plurality of through holes that are orderly arranged, a section of the second beam, the section being between a portion joined to the infrared receiver and the connection portion, has a second phononic crystal structure having a plurality of through holes that are orderly arranged, the first phononic crystal structure includes a first domain and a second domain which are phononic crystal regions, through holes of the through holes included in the first domain are orderly arranged in a first direction in plan view, through holes of the through holes included in the second domain are orderly arranged in a second direction in plan view, the second direction being different from the first direction, the second phononic crystal structure includes a third domain and a fourth domain which are phononic crystal regions, through holes of the through holes included in the third domain are orderly arranged in a third direction in plan view, and through holes of the through holes included in the fourth domain are orderly arranged in a fourth direction in plan view, the fourth direction being different from the third direction. a base substrate; a bolometer infrared receiver; a first beam; and a second beam, wherein each of the first beam and the second beam has a connection portion (16A, 16B) connected to the base substrate and/or a member on the base substrate and a separated portion away from the base substrate, and is physically joined to the infrared receiver at the separated portion, the infrared receiver is supported by the first beam and the second beam to be away from the base substrate, the infrared receiver includes a resistance change portion including a resistance change material an electrical resistance of which changes with temperature, the resistance change portion includes an amorphous semiconductor, and each of the first beam and the second beam includes a crystalline semiconductor made of a base material same as a base material of the resistance change material, and is electrically connected to the resistance change portion at the separated portion, characterized in that a section of the first beam, the section being between a portion joined to the infrared receiver and the connection portion, has a first phononic crystal structure having a plurality of through holes that are orderly arranged, a section of the second beam, the section being between a portion joined to the infrared receiver and the connection portion, has a second phononic crystal structure having a plurality of through holes that are orderly arranged, the first phononic crystal structure includes a first domain and a second domain which are phononic crystal regions, through holes of the through holes included in the first domain are orderly arranged in a first direction in plan view, through holes of the through holes included in the second domain are orderly arranged in a second direction in plan view, the second direction being different from the first direction, the second phononic crystal structure includes a third domain and a fourth domain which are phononic crystal regions, through holes of the through holes included in the third domain are orderly arranged in a third direction in plan view, and through holes of the through holes included in the fourth domain are orderly arranged in a fourth direction in plan view, the fourth direction being different from the third direction.