A sensor head for an optical measurement device and for measurement in a vacuum, the sensor head is configured to connect to a controller via a member that transmits light, the sensor head comprising: a housing; and a first lens arranged inside the housing; wherein the housing includes a first through hole communicating with a space within the housing, the housing includes a second optical path space through which light passes; the first through hole communicates with the second optical path space and passes through the housing in a direction intersecting with a direction parallel to an optical axis of the first lens; the housing includes: a first cover part covering the first lens and including a transparent member arranged intersecting with the optical axis of the first lens; and a housing body to which the first cover part is attached; the first through hole is provided in the housing body; the first lens is arranged to partition the optical path space within the housing into a first optical path space and the second optical path space; the first optical path space is located between the first cover part and the first lens; and the first through hole is provided communicating with the second optical path space; the sensor head further comprises: a lens holder arranged between an inner surface of the housing and the first lens for holding the first lens; wherein the lens holder includes a first communicating part being a groove for communicating the first optical path space and the second optical path space; a first lens fitting part having a ring shape for securing the first lens to the lens holder; a male screw provided on an outer peripheral surface of the first lens fitting part; and a female screw provided on an inner peripheral surface of the lens holder; wherein fastening together the male screw of the first lens fitting part and the female screw of the lens holder secures the first lens to the lens holder; characterized by a first lens ring arranged between the first lens and the first lens fitting part; wherein the first lens fitting part includes a second communicating part for communicating a gap with the second optical path space, the gap being created by the lens holder, the first lens, the first lens ring, and the first lens fitting part being fitted together. a housing; and a first lens arranged inside the housing; wherein the housing includes a first through hole communicating with a space within the housing, the housing includes a second optical path space through which light passes; the first through hole communicates with the second optical path space and passes through the housing in a direction intersecting with a direction parallel to an optical axis of the first lens; the housing includes: a first cover part covering the first lens and including a transparent member arranged intersecting with the optical axis of the first lens; and a housing body to which the first cover part is attached; a first cover part covering the first lens and including a transparent member arranged intersecting with the optical axis of the first lens; and a housing body to which the first cover part is attached; the first through hole is provided in the housing body; the first lens is arranged to partition the optical path space within the housing into a first optical path space and the second optical path space; the first optical path space is located between the first cover part and the first lens; and the first through hole is provided communicating with the second optical path space; the sensor head further comprises: a lens holder arranged between an inner surface of the housing and the first lens for holding the first lens; wherein the lens holder includes a first communicating part being a groove for communicating the first optical path space and the second optical path space; a first lens fitting part having a ring shape for securing the first lens to the lens holder; a male screw provided on an outer peripheral surface of the first lens fitting part; and a female screw provided on an inner peripheral surface of the lens holder; wherein fastening together the male screw of the first lens fitting part and the female screw of the lens holder secures the first lens to the lens holder; characterized by a first lens ring arranged between the first lens and the first lens fitting part; wherein the first lens fitting part includes a second communicating part for communicating a gap with the second optical path space, the gap being created by the lens holder, the first lens, the first lens ring, and the first lens fitting part being fitted together. a lens holder arranged between an inner surface of the housing and the first lens for holding the first lens; wherein the lens holder includes a first communicating part being a groove for communicating the first optical path space and the second optical path space; a first lens fitting part having a ring shape for securing the first lens to the lens holder; a male screw provided on an outer peripheral surface of the first lens fitting part; and a female screw provided on an inner peripheral surface of the lens holder; wherein fastening together the male screw of the first lens fitting part and the female screw of the lens holder secures the first lens to the lens holder; characterized by a first lens ring arranged between the first lens and the first lens fitting part; wherein the first lens fitting part includes a second communicating part for communicating a gap with the second optical path space, the gap being created by the lens holder, the first lens, the first lens ring, and the first lens fitting part being fitted together.