b coupled to the coupler 1 b of the railcar 1 that is the towed vehicle each of the first coupling portion 11 a and the second coupling portion 11 b is formed in a columnar shape from a base end portion to a center portion and is formed in a conical shape at a tip end portion a first through hole 2 and a second through hole 3 are formed on the coupler adapter 11 the coupler adapter 11 according to the present embodiment is basically the same in configuration as an existing coupler adapter which has been used so far therefore even if the holding device 100 according to the present embodiment is newly adopted it is unnecessary to change the existing coupler adapter the holding frame 12 is a member configured to directly hold the coupler adapter 11 as shown in fig4 a and 4b the holding frame 12 has a rectangular outer edge and is formed in a figure of 8 as shown in fig5 b for example the holding frame 12 includes two holding members 6 these holding members 6 are provided at positions respectively corresponding to the first coupling portion 11 a and second coupling portion 11 b of the coupler adapter each of the holding members 6 is formed in a u shape having a predetermined depth the depths of the holding members 6 respectively correspond to about half a diameter of the first coupling portion 11 a and about half a diameter of the second coupling portion 11 b as shown in fig5 b and 5c a second screw hole 5 is formed in the vicinity of one upper corner of the holding frame 12 as.