A hydraulic drive system for the pitch cylinders (4A, 4B) of a bulldozer blade apparatus can include (a) main hydraulic pumps (30A, 30B) and an assistant hydraulic pump (31) to make up the assistant hydraulic circuit, (b) variable displacement hydraulic pumps (21A, 21B), or (c) fixed displacement hydraulic pumps (30A, 30B) and a plurality of solenoid selector valves such that the pitch cylinders can be connected in series. The assistant hydraulic pump (31) is connectable to delivery lines of the main hydraulic pumps through an assistant solenoid selector valve (32) which is controlled by an external signal. The blade (10) can be formed so that a line (14) tangential to the lower edge of the curved panel of the blade is inclined rearwardly with respect to the front face (13) of the blade edge member (12). Earth-moving work can be performed by inclining the blade (10) rearwardly by an angle (.theta..sub.1) with respect to its posture in digging work, and earth-dumping work can be performed by inclining the blade (10) forwardly by an angle (.theta..sub.2) with respect to its posture in digging work. The coupling positions of the two pitch cylinders (4A, 4B) can be in asymmetrical relation to each other. Control signals can be provided by a blade lever (23), tilt/pitch changeover switch (24), and pitch speed changeover switch (25). The tilt/pitch changeover switch (24) and pitch speed changeover switch (25) can be replaced by pitch-dump selector switch (25A) and pitch-back selector switch (24A).