A fluid tank comprising a structure of a nozzle for piping provided in a tank body of the fluid tank, the structure comprising: a nozzle body including: a cylinder inserted through an interior and an exterior of the tank body via a nozzle body insertion hole in the tank body and including a male screw formed in a portion exposed to an exterior of the tank body; and a skirt expanding annularly from an end portion of the cylinder in an interior of the tank body; a sealing member interposed between an inner surface of the tank body and the skirt around a periphery of the nozzle body insertion hole; and a spacer member with an annular shape disposed around the cylinder on an outer surface of the tank body; a portion of the tank body around the nozzle body insertion hole being sandwiched by the skirt and the spacer member due to a nut being tightened onto the male screw; wherein: an inner circumferential surface side engaging portion is provided in an inner circumferential surface of the nozzle body insertion hole; and an outer circumferential surface side engaging portion configured to engage with the inner circumferential surface side engaging portion and stop rotation of the cylinder within the nozzle body insertion hole is provided on the outer circumferential surface of the cylinder. a nozzle body including: a cylinder inserted through an interior and an exterior of the tank body via a nozzle body insertion hole in the tank body and including a male screw formed in a portion exposed to an exterior of the tank body; and a skirt expanding annularly from an end portion of the cylinder in an interior of the tank body; a sealing member interposed between an inner surface of the tank body and the skirt around a periphery of the nozzle body insertion hole; and a spacer member with an annular shape disposed around the cylinder on an outer surface of the tank body; a portion of the tank body around the nozzle body insertion hole being sandwiched by the skirt and the spacer member due to a nut being tightened onto the male screw; wherein: an inner circumferential surface side engaging portion is provided in an inner circumferential surface of the nozzle body insertion hole; and an outer circumferential surface side engaging portion configured to engage with the inner circumferential surface side engaging portion and stop rotation of the cylinder within the nozzle body insertion hole is provided on the outer circumferential surface of the cylinder. a cylinder inserted through an interior and an exterior of the tank body via a nozzle body insertion hole in the tank body and including a male screw formed in a portion exposed to an exterior of the tank body; and a skirt expanding annularly from an end portion of the cylinder in an interior of the tank body; a sealing member interposed between an inner surface of the tank body and the skirt around a periphery of the nozzle body insertion hole; and a spacer member with an annular shape disposed around the cylinder on an outer surface of the tank body; a portion of the tank body around the nozzle body insertion hole being sandwiched by the skirt and the spacer member due to a nut being tightened onto the male screw; wherein: an inner circumferential surface side engaging portion is provided in an inner circumferential surface of the nozzle body insertion hole; and an outer circumferential surface side engaging portion configured to engage with the inner circumferential surface side engaging portion and stop rotation of the cylinder within the nozzle body insertion hole is provided on the outer circumferential surface of the cylinder. an inner circumferential surface side engaging portion is provided in an inner circumferential surface of the nozzle body insertion hole; and an outer circumferential surface side engaging portion configured to engage with the inner circumferential surface side engaging portion and stop rotation of the cylinder within the nozzle body insertion hole is provided on the outer circumferential surface of the cylinder.