To provide a shaft connection structure constructed to fit and mount a connection pin into connection holes without pressing it therein while effectively and easily prevent the come-off of the connection pin.

The shaft connection structure is provided for connecting first and second spool members 171, 172 to each other rockingly around their connection portion in a coaxially extending condition. At the end of the first spool member 171, a fitting recessed portion 171a is formed extending in the axial direction. At the end of the second spool member 172, a fitting protruded portion 172 is formed extending in the axial direction, which can be fitted to the fitting recessed portion. Into the first and second connection holes 171c, 172c formed passing through a site where the fitting recessed portion is fitted to the fitting protruded portion, in the direction perpendicular to the axis, the connection pin 173 is inserted to connect both spool members 171, 172 to each other rockingly around the connection pin. In a site on the outer periphery of the first spool member where the connection hole is formed, an annular holding groove 171d is formed which is recessed in the peripheral direction. A ring member 174 mounted in the holding groove covers both ends of the connection pin inserted into the connection holes to prevent the come-off of the connection pin.