Regulator of hydraulic motor for excavation

The regulator (2) comprises a servo piston (4), a first switching valve (5) and a second switching valve (7). The servo piston (4) includes a small-diameter portion (41) and a large-diameter portion (42), an annular surface of the large-diameter portion (42) faces the first pressure receiving chamber (4a), and an end surface of the large-diameter portion (42) faces the second pressure receiving chamber (4b). A first switching valve (5) is connected to an input path (3) for supplying inlet pressure to a hydraulic motor (9) and a tank path (5a), and is connected to a second pressure receiving chamber (4b) via a pressure regulating path (6). The second switching valve (7) is provided between the first flow path (61) and the second flow path (62) of the pressure regulating path (6), and the second switching valve (7) is connected to a bypass path (75) diverging from the input path (3). The second switching valve (7) connects the first flow path (61) and the second flow path (62) or connects the bypass path (75) a