An upper tool holder apparatus in a press brake includes: a holder main body having an upper tool supporting section for supporting an upper tool a lower portion of the holder main body and further having a mounting; an upper tool clamp supported to the holder main body having an engagement projection at the bottom end of the upper tool clamp which is engaged with a drop-prevention groove provided in the upper tool; a pressing section provided on a lower portion of the upper tool clamp; clamping force applying means for applying a clamping force which clamps the upper tool by pressing an upper portion of the upper tool clamp; clamp operating means for transmitting the clamping force from the clamping force applying means to the upper tool clamp and for releasing the clamping force; and a wedge piece, which is engaged with the drop-prevention groove provided in the upper tool, provided on an upper portion of the engagement projection provided on the lower portion of the upper tool clamp, a force being applied to the wedge piece in a direction where it moves forwards and backwards and it is engaged with the drop-prevention groove. In the construction above, a groove is formed in a front-and-rear direction on a center portion of a right-and-left direction of a lower portion of the mounting plate; and a right-and-left pivoting prevention member which is engaged with the groove is provided on an upper portion of the upper tool clamp.