A spectrometry device for measuring measurement target light emitted from a sample, comprising: an integrating sphere which includes an inner wall surface configured to reflect the measurement target light and an attachment hole extending outward from the inner wall surface; an adapter which includes a guide hole configured to guide the measurement target light and is disposed in the attachment hole; a plate comprising a substrate which includes a first surface configured to cover the guide hole from the outside of the integrating sphere and configured to allow the sample to be mounted thereon and a second surface disposed on the side opposite to the first surface, the substrate being made of a material transparent to the measurement target light; a holder which includes a concave portion accommodating the plate and is attached to the integrating sphere; and a spectral detector configured to detect the measurement target light output from the integrating sphere, wherein: the concave portion includes a bottom surface facing the second surface and a side surface surrounding the periphery of the plate, the bottom surface and the side surface are coated with a reflective material reflecting the measurement target light; the plate further includes a first electrode exposed to the first surface and a second electrode exposed to the second surface, and the first electrode and the second electrode are electrically connected to each other an integrating sphere which includes an inner wall surface configured to reflect the measurement target light and an attachment hole extending outward from the inner wall surface; an adapter which includes a guide hole configured to guide the measurement target light and is disposed in the attachment hole; a plate comprising a substrate which includes a first surface configured to cover the guide hole from the outside of the integrating sphere and configured to allow the sample to be mounted thereon and a second surface disposed on the side opposite to the first surface, the substrate being made of a material transparent to the measurement target light; a holder which includes a concave portion accommodating the plate and is attached to the integrating sphere; and a spectral detector configured to detect the measurement target light output from the integrating sphere, wherein: the concave portion includes a bottom surface facing the second surface and a side surface surrounding the periphery of the plate, the bottom surface and the side surface are coated with a reflective material reflecting the measurement target light; the plate further includes a first electrode exposed to the first surface and a second electrode exposed to the second surface, and the first electrode and the second electrode are electrically connected to each other the concave portion includes a bottom surface facing the second surface and a side surface surrounding the periphery of the plate, the bottom surface and the side surface are coated with a reflective material reflecting the measurement target light; the plate further includes a first electrode exposed to the first surface and a second electrode exposed to the second surface, and the first electrode and the second electrode are electrically connected to each other