A projection display device comprising: a first substrate, including a front surface on which a red light source is mounted; a second substrate, including a front surface on which a green light source is mounted; a third substrate, including a front surface on which a blue light source is mounted; a housing to which the first to third substrates are attached, the housing comprising walls comprising a first window, a second window, and a third window; an optical member accommodated in the housing; and a light modulating element attached to the housing, light emitted into the housing from the red light source, the green light source, and the blue light source being distributed by the optical member, the distributed light being converted to a prescribed display image by the light modulating element and projected externally from the housing, wherein the first to third substrates (42, 44, 45) are made of metal or filler-containing plastic compounded with a filler, the filler having a thermal conductivity higher than polycarbonate resin, and the housing is made of metal or filler-containing plastic compounded with a filler, the filler having a thermal conductivity higher than polycarbonate resin, characterised in that: parts of the front surfaces of the first to third substrates are covered with insulation layers having good electric insulation, the other parts of the front surfaces are non-insulation-layer parts, wherein the non-insulation-layer part of the first substrate is in contact with an outer surface of the walls, allowing the red light source to be seen, from the inside of the housing, through the first window wherein the non-insulation-layer part of the second substrate is in contact with an outer surface of the walls, allowing the green light source to be seen, from the inside of the housing, through the second window, wherein the non-insulation-layer part of the third substrate is in contact with an outer surface of the walls, allowing the blue light source to be seen, from the inside of the housing, through the third window. a first substrate, including a front surface on which a red light source is mounted; a second substrate, including a front surface on which a green light source is mounted; a third substrate, including a front surface on which a blue light source is mounted; a housing to which the first to third substrates are attached, the housing comprising walls comprising a first window, a second window, and a third window; an optical member accommodated in the housing; and a light modulating element attached to the housing, light emitted into the housing from the red light source, the green light source, and the blue light source being distributed by the optical member, the distributed light being converted to a prescribed display image by the light modulating element and projected externally from the housing, wherein the first to third substrates (42, 44, 45) are made of metal or filler-containing plastic compounded with a filler, the filler having a thermal conductivity higher than polycarbonate resin, and the housing is made of metal or filler-containing plastic compounded with a filler, the filler having a thermal conductivity higher than polycarbonate resin, characterised in that: parts of the front surfaces of the first to third substrates are covered with insulation layers having good electric insulation, the other parts of the front surfaces are non-insulation-layer parts, wherein the non-insulation-layer part of the first substrate is in contact with an outer surface of the walls, allowing the red light source to be seen, from the inside of the housing, through the first window wherein the non-insulation-layer part of the second substrate is in contact with an outer surface of the walls, allowing the green light source to be seen, from the inside of the housing, through the second window, wherein the non-insulation-layer part of the third substrate is in contact with an outer surface of the walls, allowing the blue light source to be seen, from the inside of the housing, through the third window. wherein the non-insulation-layer part of the first substrate is in contact with an outer surface of the walls, allowing the red light source to be seen, from the inside of the housing, through the first window wherein the non-insulation-layer part of the second substrate is in contact with an outer surface of the walls, allowing the green light source to be seen, from the inside of the housing, through the second window, wherein the non-insulation-layer part of the third substrate is in contact with an outer surface of the walls, allowing the blue light source to be seen, from the inside of the housing, through the third window.