A laser unit may include a laser chamber including a pair of discharge electrodes that are opposed to each other in a first direction with an electrode gap interposed in between and are configured to provide a discharge width in a second direction, orthogonal to the first direction, smaller than the electrode gap; and an optical resonator including a first optical member and a second optical member that are opposed to each other in a third direction orthogonal to both the first direction and the second direction with the discharge electrodes interposed in between, and configured to amplify laser light generated between the discharge electrodes and output amplified laser light, the optical resonator satisfying the following expression to configure a stable resonator in the second direction: 0