A sliding door apparatus comprising: a door (2a, 2b) that opens and closes a doorway (1 a) by being moved horizontally; a vertically elongated first housing that is disposed on a first vertical frame of a doorway frame; a vertically elongated second housing that is disposed on a second vertical frame of the doorway frame; a first light emitter that is disposed in the first housing, and that comprises a vertically long and continuous first light-emitting surface; a second light emitter that is disposed in the second housing, and that comprises a vertically long and continuous second light-emitting surface; a first imaging means that is disposed in the first housing, and that captures an image of the second light-emitting surface; a second imaging means that is disposed in the second housing, and that captures an image of the first light-emitting surface; and an image processing portion (11a, 12a) that determines presence or absence of an object in the doorway (1 a) based on a signal from the first and second imaging means (7 and 9), characterised in that, the first and second housings (4 and 5) each comprise: a housing main body that has an opening on a front surface; and a partitioning plate that is disposed at an intermediate portion in a width direction inside the housing main body; the housing main body is divided internally into a light emitter chamber (21 a) and an imaging means chamber (21 b) by the partitioning plate; the first and second light emitters (6 and 8) are disposed in the light emitter chambers (21 a); and the first and second imaging means (7 and 9) are disposed in the imaging means chambers (21 b). a door (2a, 2b) that opens and closes a doorway (1 a) by being moved horizontally; a vertically elongated first housing that is disposed on a first vertical frame of a doorway frame; a vertically elongated second housing that is disposed on a second vertical frame of the doorway frame; a first light emitter that is disposed in the first housing, and that comprises a vertically long and continuous first light-emitting surface; a second light emitter that is disposed in the second housing, and that comprises a vertically long and continuous second light-emitting surface; a first imaging means that is disposed in the first housing, and that captures an image of the second light-emitting surface; a second imaging means that is disposed in the second housing, and that captures an image of the first light-emitting surface; and an image processing portion (11a, 12a) that determines presence or absence of an object in the doorway (1 a) based on a signal from the first and second imaging means (7 and 9), characterised in that, the first and second housings (4 and 5) each comprise: a housing main body that has an opening on a front surface; and a partitioning plate that is disposed at an intermediate portion in a width direction inside the housing main body; a housing main body that has an opening on a front surface; and a partitioning plate that is disposed at an intermediate portion in a width direction inside the housing main body; the housing main body is divided internally into a light emitter chamber (21 a) and an imaging means chamber (21 b) by the partitioning plate; the first and second light emitters (6 and 8) are disposed in the light emitter chambers (21 a); and the first and second imaging means (7 and 9) are disposed in the imaging means chambers (21 b).