Shock absorber

A shock absorber comprising:

• a main piston which is mounted on a piston rod reciprocating within a cylinder, slidingly reciprocates within the cylinder while contacting an inner periphery of the cylinder, and partitions the cylinder into upper and lower chambers;
• a communication passage which is formed in the piston rod to communicate the upper chamber with the lower chamber, and penetrates from an upper side of the main piston to a lower side of the piston rod;
• a housing which is mounted on a lower end of the piston rod to form an internal space, a communication hole connected to the lower chamber being formed in a bottom surface of the housing;
• a hollow elevating piece which moves upward and downward while contacting an inner periphery of the housing and partitions the housing into upper and lower spaces;
• a plurality of slits which are formed in an outer periphery of the elevating piece and allow the working fluid to flow into the lower space so as to reduce a damping force when a small amount of a working fluid is introduced into the housing;
• and
• a deformation film which is mounted along an inner periphery of the elevating piece and allows an elastic deformation to extend toward a bottom side of the housing so as to close the communication hole when the elevating piece moves downward due to an increase in the amount of the working fluid introduced into the housing.