A beam splitting device for recording in-line holograms comprising: a phase modulating device which provides a phase difference between a first polarization component contained in incident light and having a plane of polarization parallel to a first direction and a second polarization component contained in the incident light and having a plane of polarization parallel to a second direction perpendicular to the first direction; at least one birefringent lens (12, 12-1, 12-2, 41, 42) which splits the incident light into a first beam having the first polarization component and a second beam having the second polarization component, and which causes both the first beam and the second beam to emerge along a common optical axis, and converting at least one of the first and second beams into a convergent light, and a polarizing plate which is disposed downstream the at least one birefringent lens, and which is arranged in the common path of each of the first and second beams, to allow a polarization component parallel in a direction that bisects an angle that the first direction makes with the second direction to pass through, wherein the phase modulating device includes a liquid crystal layer which contains liquid crystal molecules and which is aligned so that long axes of the liquid crystal molecules are oriented in the first direction, and two transparent electrodes (23, 24) which are disposed opposite each other by sandwiching the liquid crystal layer therebetween, and wherein the phase modulating device shifts a phase of the first polarization component according to a voltage applied between the two transparent electrodes (23, 24) to cause a phase difference to occur between the first polarization component and the second polarization component. a phase modulating device which provides a phase difference between a first polarization component contained in incident light and having a plane of polarization parallel to a first direction and a second polarization component contained in the incident light and having a plane of polarization parallel to a second direction perpendicular to the first direction; at least one birefringent lens (12, 12-1, 12-2, 41, 42) which splits the incident light into a first beam having the first polarization component and a second beam having the second polarization component, and which causes both the first beam and the second beam to emerge along a common optical axis, and converting at least one of the first and second beams into a convergent light, and a polarizing plate which is disposed downstream the at least one birefringent lens, and which is arranged in the common path of each of the first and second beams, to allow a polarization component parallel in a direction that bisects an angle that the first direction makes with the second direction to pass through, wherein the phase modulating device includes a liquid crystal layer which contains liquid crystal molecules and which is aligned so that long axes of the liquid crystal molecules are oriented in the first direction, and two transparent electrodes (23, 24) which are disposed opposite each other by sandwiching the liquid crystal layer therebetween, and wherein the phase modulating device shifts a phase of the first polarization component according to a voltage applied between the two transparent electrodes (23, 24) to cause a phase difference to occur between the first polarization component and the second polarization component.