Exhaust passage control valve 10 may comprise housing 30, valve member 20,
and helical torsion spring 40. Housing 30 has an exhaust passage. Exhaust
gas from an internal combustion engine flows through the exhaust passage
of the housing 30. Valve member 20 opens and closes the exhaust passage
of the housing. Helical torsion spring 40 may be disposed at the opposite
side of the valve member from the housing side thereof. Helical torsion
spring 40 comprises a coil part wherein spring wires have been wound in a
coil shape, and arms formed at both ends of the coil part. The coil part
may be disposed at approximately the center of the valve member. When the
arms bend with respect to the coil part, the counter-force of this
bending energizes the valve member towards a closing side. The spring
mounting member may be arranged and constructed to adjust a position in
which the spring mounting member is mounted on the housing such that a
rotation angle of the arms can be changed.