A seat adjustment mechanism, adjusting an angle formed between first and second seat members (101, 102) rotatably connected to each other, comprising: a first link member adapted to be connected to the first seat member and including a first end rotatably supported by the first seat member; and a drive device; characterized in that it further comprises: a second link member adapted to be rotatably connected to the second seat member and including a first end rotatably supported by the second seat member and a second end rotatably connected to the first link member; and an extending and retracting device driven by the drive device and extending and retracting linearly, wherein one of the drive device and the extending and retracting device is rotatably connected to a second end of the first link member and the other of the drive device and the extending and retracting device is rotatably connected to the second seat member, wherein considering that a connecting point between the first link member and the second link member is defined as a connecting point P, a connecting point between the first seat member and the first link member is defined as a connecting point Q, a connecting point between the second seat member and the second link member is defined as a connecting point R, a connecting point between the first link member and one of the drive device and the extending and retracting device is defined as a connecting point S, a connecting point between the second seat member and the other of the drive device and the extending and retracting device is defined as a connecting point T, a line linearly passing through the connecting points Q and R is defined as a line L1, and a line linearly passing through the connecting points S and T is defined as a line L2, the first and second link members (110, 120), the first link member and one of the drive device and the extending and retracting device, and the second link and the other of the drive device and the extending and retracting device are connected to each other so that a ratio (a/b) of a distance (a) from the connecting point P to the line L1 relative to a distance (b) from the connecting point P to the line L2 is set to be less than one, and wherein the drive device is driven to move the extending and retracting device linearly to rotate the first link member relative to the second link member to thereby generate a relative rotation between the first seat member and the second seat member in order to adjust the angle between the first and second seat members (101, 102). a first link member adapted to be connected to the first seat member and including a first end rotatably supported by the first seat member; and a drive device; a second link member adapted to be rotatably connected to the second seat member and including a first end rotatably supported by the second seat member and a second end rotatably connected to the first link member; and an extending and retracting device driven by the drive device and extending and retracting linearly, wherein one of the drive device and the extending and retracting device is rotatably connected to a second end of the first link member and the other of the drive device and the extending and retracting device is rotatably connected to the second seat member, wherein considering that a connecting point between the first link member and the second link member is defined as a connecting point P, a connecting point between the first seat member and the first link member is defined as a connecting point Q, a connecting point between the second seat member and the second link member is defined as a connecting point R, a connecting point between the first link member and one of the drive device and the extending and retracting device is defined as a connecting point S, a connecting point between the second seat member and the other of the drive device and the extending and retracting device is defined as a connecting point T, a line linearly passing through the connecting points Q and R is defined as a line L1, and a line linearly passing through the connecting points S and T is defined as a line L2, the first and second link members (110, 120), the first link member and one of the drive device and the extending and retracting device, and the second link and the other of the drive device and the extending and retracting device are connected to each other so that a ratio (a/b) of a distance (a) from the connecting point P to the line L1 relative to a distance (b) from the connecting point P to the line L2 is set to be less than one, and wherein the drive device is driven to move the extending and retracting device linearly to rotate the first link member relative to the second link member to thereby generate a relative rotation between the first seat member and the second seat member in order to adjust the angle between the first and second seat members (101, 102).