A medical device for incising a substance inside a biological lumen. The medical device includes a tubular drive shaft that is rotatable, an intermediate portion connected to the drive shaft, at least one strut interlocked with the drive shaft, a tubular linear motion shaft inside of the drive shaft, and a tubular interlock portion. The strut is rotatable with the drive shaft and is expandable radially outward in response to outward expansion of the intermediate portion. The linear motion shaft is movable relative to the drive shaft in the axial direction to cause the strut to expand radially outward. The tubular interlock portion interlocks the drive shaft and the linear motion shaft while maintaining liquid-tight properties. The tubular interlock portion is stretchable in the axial direction.