Provided is a shaft capable of suppressing the rise in operation resistance when pushed and pulled even inside an extremely winding blood vessel to secure sufficient torque transmission characteristics so that operability is improved, and a guidewire employing the shaft. A shaft 10 is twisted along a longitudinal direction, having a cross section taking the form of an approximately rectangular shape in a direction vertical to the longitudinal direction. Moreover, the cross section of the shaft 10 has a projection 14 projected arcuately.
