An endoscopic diagnostic apparatus, comprising: an endoscope arranged and adapted to inject water from a distal end of an insertion part; a scope hood attached to the distal end of the insertion part of the endoscope; and a processor device; characterised in that: the processor device comprises: water injection amount detection means configured to detect an amount of water injected from the distal end of the insertion part; position detection means configured to detect, from an image captured by the endoscope, a position of a distal end portion of the scope hood on the image; model detection means configured to detect at least one of a model of the endoscope or a model of the scope hood; space volume detection means configured to detect a volume of an internal space of the scope hood, which is formed by a distal end surface of the insertion part of the endoscope and the scope hood, using the position of the distal end portion of the scope hood detected by the position detection means and at least one of the model of the endoscope or the model of the scope hood detected by the model detection means; and lesion part volume detection means configured to detect a volume of a lesion part from the water injection amount detected by the water injection amount detection means and the volume of the internal space of the scope hood detected by the space volume detection means. an endoscope arranged and adapted to inject water from a distal end of an insertion part; a scope hood attached to the distal end of the insertion part of the endoscope; and a processor device; characterised in that: the processor device comprises: water injection amount detection means configured to detect an amount of water injected from the distal end of the insertion part; position detection means configured to detect, from an image captured by the endoscope, a position of a distal end portion of the scope hood on the image; model detection means configured to detect at least one of a model of the endoscope or a model of the scope hood; space volume detection means configured to detect a volume of an internal space of the scope hood, which is formed by a distal end surface of the insertion part of the endoscope and the scope hood, using the position of the distal end portion of the scope hood detected by the position detection means and at least one of the model of the endoscope or the model of the scope hood detected by the model detection means; and lesion part volume detection means configured to detect a volume of a lesion part from the water injection amount detected by the water injection amount detection means and the volume of the internal space of the scope hood detected by the space volume detection means. water injection amount detection means configured to detect an amount of water injected from the distal end of the insertion part; position detection means configured to detect, from an image captured by the endoscope, a position of a distal end portion of the scope hood on the image; model detection means configured to detect at least one of a model of the endoscope or a model of the scope hood; space volume detection means configured to detect a volume of an internal space of the scope hood, which is formed by a distal end surface of the insertion part of the endoscope and the scope hood, using the position of the distal end portion of the scope hood detected by the position detection means and at least one of the model of the endoscope or the model of the scope hood detected by the model detection means; and lesion part volume detection means configured to detect a volume of a lesion part from the water injection amount detected by the water injection amount detection means and the volume of the internal space of the scope hood detected by the space volume detection means.