A method for adjusting a valve clearance in a cylinder head using a rocker arm of a support point adjustable type. In the method, an adjustment screw is rotated in one direction until a camshaft comes in contact with a cam shaft contact section to make the amount of valve opening zero, then further rotated until the valve is released with a certain valve opening amount, and after that, rotated in a reverse direction by a certain rotation angle and accordingly loosened until a desired valve clearance value is obtained. In the process above, the method determines a first rotation angle of the adjustment screw necessary for the adjustment screw to move from a position where the valve is released with the certain valve opening amount to a position where the camshaft comes in contact with the camshaft contact section. Then, the method determines a second rotation angle of the adjustment screw necessary for the adjustment screw to move from the position where the camshaft comes in contact with the camshaft contact section to a position where the desired valve clearance value can be obtained. After that, the method rotates the adjustment screw in the reverse direction by a given rotation angle that is a sum of the first and second rotation angles.