An abnormality detection system, comprising: a laser transmission tube coupled with a laser treatment unit, oscillating laser light, to transmit the laser light; and a cooling portion fluid change detection portion detecting a change in a pressure of a cooling fluid flowing through a cooling space (T1, T2) in the laser transmission tube, the laser transmission tube including: a lightguide tube having a lightguide space formed therein, through which the laser light is guided, the lightguide space being formed in a longitudinal direction, and an outer case enclosing an outer circumferential surface of the lightguide tube and extending in the longitudinal direction, the cooling space (T1, T2) being formed in the longitudinal direction between the lightguide tube and the outer case, and the cooling portion fluid change detection portion detecting the change in the pressure of the cooling fluid flowing through the cooling space (T1, T2) to detect an abnormality, wherein the cooling space includes: a forward-direction space causing the cooling fluid to flow in the longitudinal direction in a forward direction from a base end toward a tip end, a backward-direction space causing the cooling fluid, after the cooling fluid flows through the forward-direction space, to flow in the longitudinal direction in a backward direction from the tip end toward the base end, the forward-direction space being formed outer to the backward-direction space, and a communication space communicating the forward-direction space and the backward-direction space to each other at the tip end, and wherein the cooling portion fluid change detection portion detects the change in the pressure of the cooling fluid in the backward-direction space. a laser transmission tube coupled with a laser treatment unit, oscillating laser light, to transmit the laser light; and a cooling portion fluid change detection portion detecting a change in a pressure of a cooling fluid flowing through a cooling space (T1, T2) in the laser transmission tube, the laser transmission tube including: a lightguide tube having a lightguide space formed therein, through which the laser light is guided, the lightguide space being formed in a longitudinal direction, and an outer case enclosing an outer circumferential surface of the lightguide tube and extending in the longitudinal direction, a lightguide tube having a lightguide space formed therein, through which the laser light is guided, the lightguide space being formed in a longitudinal direction, and an outer case enclosing an outer circumferential surface of the lightguide tube and extending in the longitudinal direction, the cooling space (T1, T2) being formed in the longitudinal direction between the lightguide tube and the outer case, and the cooling portion fluid change detection portion detecting the change in the pressure of the cooling fluid flowing through the cooling space (T1, T2) to detect an abnormality, wherein the cooling space includes: a forward-direction space causing the cooling fluid to flow in the longitudinal direction in a forward direction from a base end toward a tip end, a backward-direction space causing the cooling fluid, after the cooling fluid flows through the forward-direction space, to flow in the longitudinal direction in a backward direction from the tip end toward the base end, the forward-direction space being formed outer to the backward-direction space, and a communication space communicating the forward-direction space and the backward-direction space to each other at the tip end, and a forward-direction space causing the cooling fluid to flow in the longitudinal direction in a forward direction from a base end toward a tip end, a backward-direction space causing the cooling fluid, after the cooling fluid flows through the forward-direction space, to flow in the longitudinal direction in a backward direction from the tip end toward the base end, the forward-direction space being formed outer to the backward-direction space, and a communication space communicating the forward-direction space and the backward-direction space to each other at the tip end, and wherein the cooling portion fluid change detection portion detects the change in the pressure of the cooling fluid in the backward-direction space.