A turbocharger, comprising: a compressor wheel; a turbine wheel configured to rotate with the compressor wheel; a turbine housing disposed so as to cover the turbine wheel; a bearing (15A, 15B) supporting a rotational shaft of the turbine wheel rotatably; and a bearing housing accommodating the bearing (15A, 15B), wherein one of the turbine housing or the bearing housing includes a fin portion (60, 60A, 60B) protruding toward the other one of the turbine housing or the bearing housing so as to extend along an axial direction of the rotational shaft, and wherein, between the turbine housing and the bearing housing, a cavity (80A, 80B) is formed on each side of the fin portion (60, 60A, 60B) with respect to a radial direction of the rotational shaft, wherein the turbocharger further comprises a fastening portion configured to fasten the turbine housing and the bearing housing, wherein the fastening portion is configured to apply a fastening force in the axial direction to the turbine housing and the bearing housing so that a tip of the fin portion (60, 60A, 60B) makes contact with the other one of the turbine housing or the bearing housing, wherein the turbocharger further includes a back plate (70, 70A, 70B) disposed on a back-surface side of the turbine wheel, and wherein the back plate (70, 70A, 70B) includes a first end and a second end with respect to the radial direction, and the back plate (70, 70A, 70B) is held between the turbine housing and the bearing housing so that the first end is in contact with the turbine housing and the second end is in contact with the other one of the bearing housing, characterized in that the other one of the turbine housing or the bearing housing includes a groove which receives the tip of the fin portion (60, 60A, 60B), and the turbocharger further comprises a heat insulator or a filling material disposed inside the groove. a compressor wheel; a turbine wheel configured to rotate with the compressor wheel; a turbine housing disposed so as to cover the turbine wheel; a bearing (15A, 15B) supporting a rotational shaft of the turbine wheel rotatably; and a bearing housing accommodating the bearing (15A, 15B), wherein one of the turbine housing or the bearing housing includes a fin portion (60, 60A, 60B) protruding toward the other one of the turbine housing or the bearing housing so as to extend along an axial direction of the rotational shaft, and wherein, between the turbine housing and the bearing housing, a cavity (80A, 80B) is formed on each side of the fin portion (60, 60A, 60B) with respect to a radial direction of the rotational shaft, wherein the turbocharger further comprises a fastening portion configured to fasten the turbine housing and the bearing housing, wherein the fastening portion is configured to apply a fastening force in the axial direction to the turbine housing and the bearing housing so that a tip of the fin portion (60, 60A, 60B) makes contact with the other one of the turbine housing or the bearing housing, wherein the turbocharger further includes a back plate (70, 70A, 70B) disposed on a back-surface side of the turbine wheel, and wherein the back plate (70, 70A, 70B) includes a first end and a second end with respect to the radial direction, and the back plate (70, 70A, 70B) is held between the turbine housing and the bearing housing so that the first end is in contact with the turbine housing and the second end is in contact with the other one of the bearing housing, characterized in that the other one of the turbine housing or the bearing housing includes a groove which receives the tip of the fin portion (60, 60A, 60B), and the turbocharger further comprises a heat insulator or a filling material disposed inside the groove.