A saddle-riding-type electric vehicle fuel cell stack fixation structure, comprising: a fuel cell stack; and a vehicle body frame that supports the fuel cell stack, wherein the vehicle body frame includes: a pair of right and left main frames that extend rearward from a head pipe and that are arranged on an outer side in a vehicle width direction of the fuel cell stack; a pair of right and left downward frames that extend rearward from the head pipe and that are arranged below the pair of right and left main frames; and a cross member (31, 32) that bridges a space in a vehicle width direction between at least the right and left downward frames and that fixes the fuel cell stack, a vehicle component accommodation part that is arranged below the downward frame and that accommodates a vehicle component (13, 14, 15, 16); and an accommodation part support member that is attached to the vehicle body frame and that supports the vehicle component accommodation part, wherein the cross member (31, 32) includes: a lower cross member that bridges a space in a vehicle width direction between the right and left downward frames, characterized in that the cross member (31, 32) further includes: an upper cross member that bridges a space in a vehicle width direction between the left and right main frames, and the upper cross member is lighter than the lower cross member. a fuel cell stack; and a vehicle body frame that supports the fuel cell stack, wherein the vehicle body frame includes: a pair of right and left main frames that extend rearward from a head pipe and that are arranged on an outer side in a vehicle width direction of the fuel cell stack; a pair of right and left downward frames that extend rearward from the head pipe and that are arranged below the pair of right and left main frames; and a cross member (31, 32) that bridges a space in a vehicle width direction between at least the right and left downward frames and that fixes the fuel cell stack, a vehicle component accommodation part that is arranged below the downward frame and that accommodates a vehicle component (13, 14, 15, 16); and an accommodation part support member that is attached to the vehicle body frame and that supports the vehicle component accommodation part, wherein the cross member (31, 32) includes: a lower cross member that bridges a space in a vehicle width direction between the right and left downward frames, characterized in that the cross member (31, 32) further includes: an upper cross member that bridges a space in a vehicle width direction between the left and right main frames, and the upper cross member is lighter than the lower cross member. a pair of right and left main frames that extend rearward from a head pipe and that are arranged on an outer side in a vehicle width direction of the fuel cell stack; a pair of right and left downward frames that extend rearward from the head pipe and that are arranged below the pair of right and left main frames; and a cross member (31, 32) that bridges a space in a vehicle width direction between at least the right and left downward frames and that fixes the fuel cell stack, a vehicle component accommodation part that is arranged below the downward frame and that accommodates a vehicle component (13, 14, 15, 16); and an accommodation part support member that is attached to the vehicle body frame and that supports the vehicle component accommodation part, wherein the cross member (31, 32) includes: a lower cross member that bridges a space in a vehicle width direction between the right and left downward frames, characterized in that the cross member (31, 32) further includes: an upper cross member that bridges a space in a vehicle width direction between the left and right main frames, and the upper cross member is lighter than the lower cross member. a lower cross member that bridges a space in a vehicle width direction between the right and left downward frames, characterized in that the cross member (31, 32) further includes: an upper cross member that bridges a space in a vehicle width direction between the left and right main frames, and the upper cross member is lighter than the lower cross member. an upper cross member that bridges a space in a vehicle width direction between the left and right main frames, and the upper cross member is lighter than the lower cross member.