Provided is a voltage regulator capable of enabling overcurrent protection in a state in which an output current is large even if an inputoutput voltage difference is small, without waiting until the output voltage decreases. The shock absorber includes a piston, a working cylinder for housing the piston; and a rod one end of which is attached to the piston and the other end of which projects from the working cylinder; wherein a friction coefficient between the piston and the working cylinder is represented by the formula 3h2rl. The second linking member has a pressing lever that is in contact with the flexible member. When the video card is written to or read from, the malfunctioning memory bank is not written to or read from according a bank address and an offset address of the malfunctioning memory bank and data is written to or read from other memory bank that are functioning. A visualization catheter also is provided for use ensuring accurate measurement of a lesion and ensuring delivery and placement of the vascular prosthesis.