To provide a new mandrel adaptable to the manufacture of a branch hose constituted by branching a sub-hose from a bent main hose.

The mandrel 100 for manufacturing the branch hose is constituted by filling a hollow tube main body 114 having flexibility with a filler 120 and maintaining the contour shape thereof by the filler 120. Since the filler 120 is formed into a suspension high in concentration containing sand as fixing particles, it shows dilatancy increased in apparent viscosity accompanied by an increase in deviation stress. Accordingly, the flow of the filler 120 is brought about when the mandrel is inserted because the apparent viscosity is low and the mandrel can be inserted so as to follow the bent hose locus of the main hose. On the other hand, since the apparent viscosity of the filler 120 is increased by the rise in pressure accompanied by injection when a cover part is formed by injecting a rubber material in a branch place, the contour shape of the main hose is kept against the force accompanied by injection.

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