Abstract: This laser gas analysis device compensates distortion of a laser beam and can place a detector depending on the wavelength used. A transmitter side process window unit consists of two wedge-shaped glass substrates that are positioned to have a space with an appropriate length along a laser propagation direction, and sends the laser beam from a transmitter unit to a measuring space. A receiver side process window unit is configured the same as the transmitter side process window unit, and sends the laser beam passed through the measuring space to a receiver unit. The outer surfaces of the two wedge-shaped glass substrates with respect to the space in between are placed to be parallel each other, and accordingly the inner surfaces are also parallel each other. The distance between the two wedge-shaped glass substrates in the laser propagation direction is determined so as to avoid optical interferences of the laser.