A vehicle allocation support system that supports work of allocating a vehicle to a train of a railroad, the system comprising: a constraint management unit configured to manage a constraint condition indicating an item to be satisfied when allocating a vehicle at a vehicle yard to a train, the constraint condition being determined for each vehicle yard, and a facility condition indicating a facility to be included in a vehicle to be allocated to a train, the facility condition being determined for each time and/or route; a vehicle candidate extraction unit configured to extract a candidate of a vehicle to be allocated to the train on a train diagram, the candidate being extracted by searching for a vehicle that is allocable to the train on the train diagram so as to satisfy the constraint condition and the facility condition and to be capable of transporting a number of passengers with demand, when information on the number of passengers with demand, which is a number of passengers that needs to be transportable by the train, is given together with an allocation implementation request to implement allocation of a vehicle to a train on the train diagram; and an influence determination unit configured to calculate an operation cost for the extracted candidate based on influence degrees, which are degrees of influence on a shunting plan which is a plan concerning circulation of vehicles, a crew plan which is a plan concerning an allocation of crews to a train, and a work plan which is a plan concerning work including a vehicle inspection; wherein the vehicle allocation support system is configured to display the operation cost relating to the extracted candidate on a display device; wherein the influence determination unit is further configured to calculate each of the degrees of influence on the shunting plan, the crew plan and the work plan for the extracted candidates, and to calculate the operation cost by totaling the influence degree on the shunting plan, the influence degree on the crew plan, and the influence degree on the work plan, wherein the influence determination unit is further configured to specify a change generated in each of the shunting plan, the crew plan, and the work plan when a vehicle as the extracted candidate is allocated to the train, and to calculate cost required for the specified change as the operation cost. a constraint management unit configured to manage a constraint condition indicating an item to be satisfied when allocating a vehicle at a vehicle yard to a train, the constraint condition being determined for each vehicle yard, and a facility condition indicating a facility to be included in a vehicle to be allocated to a train, the facility condition being determined for each time and/or route; a vehicle candidate extraction unit configured to extract a candidate of a vehicle to be allocated to the train on a train diagram, the candidate being extracted by searching for a vehicle that is allocable to the train on the train diagram so as to satisfy the constraint condition and the facility condition and to be capable of transporting a number of passengers with demand, when information on the number of passengers with demand, which is a number of passengers that needs to be transportable by the train, is given together with an allocation implementation request to implement allocation of a vehicle to a train on the train diagram; and an influence determination unit configured to calculate an operation cost for the extracted candidate based on influence degrees, which are degrees of influence on a shunting plan which is a plan concerning circulation of vehicles, a crew plan which is a plan concerning an allocation of crews to a train, and a work plan which is a plan concerning work including a vehicle inspection; wherein the vehicle allocation support system is configured to display the operation cost relating to the extracted candidate on a display device; wherein the influence determination unit is further configured to calculate each of the degrees of influence on the shunting plan, the crew plan and the work plan for the extracted candidates, and to calculate the operation cost by totaling the influence degree on the shunting plan, the influence degree on the crew plan, and the influence degree on the work plan, wherein the influence determination unit is further configured to specify a change generated in each of the shunting plan, the crew plan, and the work plan when a vehicle as the extracted candidate is allocated to the train, and to calculate cost required for the specified change as the operation cost.