A beam combining/splitting modulator comprising: a transmissive phase spatial light modulator including first and second modulation regions (111, 112) for independently modulating a phase of incident light and configured to pass incident light as polarized light with a predetermined polarized state; a polarization converter disposed at a side of an emitting surface of the transmissive phase spatial light modulator, and including a first transmissive region for polarizing and converting light incident from the first modulation region to have a first polarization and a second transmissive region for polarizing and converting light incident from the second modulation region to have a second polarization; a birefringence modulator disposed at the side of an emitting surface of the polarization converter and including a liquid crystal layer in which birefringence occurs according to a voltage applied thereto; and a polarizer disposed at the side of an emitting surface of the birefringence modulator; wherein a polarization axis of the polarizer is inclined with respect to the first and second polarization; characterized in that the birefringence modulator is configured to switch between a first state in which birefringence occurs and a second state in which birefringence does not occur; wherein, when the birefringence modulator is in the first state, a light path of at least one light of the light incident from the first modulation region and the light incident from the second modulation region is changed in the birefringence modulator, the incident lights are combined, and the combined light is emitted from the birefringence modulator, and when the birefringence modulator is in the second state, the light incident from the first modulation region and the light incident from the second modulation region are emitted from the birefringence modulator without any change of light paths thereof. a transmissive phase spatial light modulator including first and second modulation regions (111, 112) for independently modulating a phase of incident light and configured to pass incident light as polarized light with a predetermined polarized state; a polarization converter disposed at a side of an emitting surface of the transmissive phase spatial light modulator, and including a first transmissive region for polarizing and converting light incident from the first modulation region to have a first polarization and a second transmissive region for polarizing and converting light incident from the second modulation region to have a second polarization; a birefringence modulator disposed at the side of an emitting surface of the polarization converter and including a liquid crystal layer in which birefringence occurs according to a voltage applied thereto; and a polarizer disposed at the side of an emitting surface of the birefringence modulator; wherein a polarization axis of the polarizer is inclined with respect to the first and second polarization; characterized in that the birefringence modulator is configured to switch between a first state in which birefringence occurs and a second state in which birefringence does not occur; wherein, when the birefringence modulator is in the first state, a light path of at least one light of the light incident from the first modulation region and the light incident from the second modulation region is changed in the birefringence modulator, the incident lights are combined, and the combined light is emitted from the birefringence modulator, and when the birefringence modulator is in the second state, the light incident from the first modulation region and the light incident from the second modulation region are emitted from the birefringence modulator without any change of light paths thereof.