A framer which is connected to a plurality of transmitters that multicarrier-transmit a plurality of parallel signals by optical subcarriers, the framer comprising: a storage unit configured to store time slot information indicating a correspondence between time slots in a signal frame and the optical subcarriers which are used to transmit parallel signals including data set in the time slots and path accommodation information indicating a correspondence between paths allocated to a client signal and the time slots in the signal frame; an allocation processing unit configured to select, on the basis of empty time slots which are not allocated to any path indicated by the path accommodation information and the optical subcarriers corresponding to the empty time slots indicated by the time slot information, time slots to be allocated to a path to be accommodated from the empty time slots and to set a correspondence between the path to be accommodated and the selected time slots as the path accommodation information; a multiplexing unit configured to set one or more received client signals to the time slots in the signal frame on the basis of the correspondence between the paths of the client signal and the time slots which is indicated by the path accommodation information; and a transmission signal generating unit configured to divide the signal frame to which the client signal is set by the multiplexing unit to generate a plurality of parallel signals and to output the plurality of parallel signals to the plurality of transmitters that transmit the plurality of parallel signals using the optical subcarriers corresponding to the plurality of parallel signals, characterized in that: the allocation processing unit determines whether there is a transmitter among the plurality of transmitters in which the number of the empty time slots is equal to or greater than the number of time slots which it is necessary to allocate to the path to be accommodated, when there is the transmitter, the allocation processing unit selects time slots from the empty time slots of the transmitter, and when there is not the transmitter and when there are a plurality of allocation patterns in which the path to be accommodated can be allocated to minimize the number of optical subcarriers to be used, the allocation processing unit selects empty time slots of an allocation pattern including the signal frame in which the number of the empty time slots is the smallest among the plurality of allocation patterns. a storage unit configured to store time slot information indicating a correspondence between time slots in a signal frame and the optical subcarriers which are used to transmit parallel signals including data set in the time slots and path accommodation information indicating a correspondence between paths allocated to a client signal and the time slots in the signal frame; an allocation processing unit configured to select, on the basis of empty time slots which are not allocated to any path indicated by the path accommodation information and the optical subcarriers corresponding to the empty time slots indicated by the time slot information, time slots to be allocated to a path to be accommodated from the empty time slots and to set a correspondence between the path to be accommodated and the selected time slots as the path accommodation information; a multiplexing unit configured to set one or more received client signals to the time slots in the signal frame on the basis of the correspondence between the paths of the client signal and the time slots which is indicated by the path accommodation information; and a transmission signal generating unit configured to divide the signal frame to which the client signal is set by the multiplexing unit to generate a plurality of parallel signals and to output the plurality of parallel signals to the plurality of transmitters that transmit the plurality of parallel signals using the optical subcarriers corresponding to the plurality of parallel signals, characterized in that: the allocation processing unit determines whether there is a transmitter among the plurality of transmitters in which the number of the empty time slots is equal to or greater than the number of time slots which it is necessary to allocate to the path to be accommodated, when there is the transmitter, the allocation processing unit selects time slots from the empty time slots of the transmitter, and when there is not the transmitter and when there are a plurality of allocation patterns in which the path to be accommodated can be allocated to minimize the number of optical subcarriers to be used, the allocation processing unit selects empty time slots of an allocation pattern including the signal frame in which the number of the empty time slots is the smallest among the plurality of allocation patterns. the allocation processing unit determines whether there is a transmitter among the plurality of transmitters in which the number of the empty time slots is equal to or greater than the number of time slots which it is necessary to allocate to the path to be accommodated, when there is the transmitter, the allocation processing unit selects time slots from the empty time slots of the transmitter, and when there is not the transmitter and when there are a plurality of allocation patterns in which the path to be accommodated can be allocated to minimize the number of optical subcarriers to be used, the allocation processing unit selects empty time slots of an allocation pattern including the signal frame in which the number of the empty time slots is the smallest among the plurality of allocation patterns.