An optical transmission device includes: a switching configured to be capable of switching a transmission path to which light is input from a first transmission path to a second transmission path; a first calculation unit configured to calculate, based on a difference between a first light level of the first transmission path and a second light level of the second transmission path, a first control amount for the second light level; and a control unit configured to perform a first control in which the second light level is decreased or increased based on the first control amount upon switching of the transmission path.