A spectrometer comprises a package having a stem and a cap, an optical unit arranged on the stem, and a lead pin penetrating through the stem. The optical unit has a dispersive part for dispersing and reflecting light entering from a light entrance part of the cap, a light detection element for detecting the light dispersed and reflected by the dispersive part, a support for supporting the light detection element such as to form a space between the dispersive part and the light detection element, a projection projecting from the support, and a wiring electrically connected to the light detection element. The projection is arranged at such a position as to be separated from the stem. The lead pin is electrically connected to the second terminal part while being disposed to the projection.