A hydraulic pressure control device (1, 2) used in a brake system capable of executing anti-lock brake control and mounted to a handlebar of a straddle-type vehicle, the hydraulic pressure control device (1, 2) having a configuration in which a brake fluid released from a wheel cylinder during pressure decrease in the anti-lock brake control is stored in an accumulator and the brake fluid in the accumulator is pumplessly discharged out of the accumulator and comprising: a master cylinder-integrated base body where a piston mounting hole where a piston of a master cylinder is provided so as to be capable of reciprocating, a reservoir tank for brake fluid storage connected to the piston mounting hole, and an internal flow path as a part of a brake fluid flow path allowing the piston mounting hole and the wheel cylinder to communicate with each other are formed; an inlet valve provided in an inlet valve mounting hole formed in the base body so as to be capable of reciprocating and opening and closing a part of the internal flow path through which a brake fluid flowing from the piston mounting hole to the wheel cylinder passes; and an outlet valve provided in an outlet valve mounting hole formed in the base body so as to be capable of reciprocating and opening and closing a part of the internal flow path through which a brake fluid flowing from the wheel cylinder to the accumulator passes, wherein the inlet valve mounting hole and the outlet valve mounting hole are open on a second surface in a case where a surface of the base body where an opening portion of the reservoir tank is formed is a first surface and a surface of the base body opposite to the first surface is the second surface, characterized in that the hydraulic pressure control device (1, 2) further comprises a pressure sensor provided in a pressure sensor mounting hole formed in the base body and detecting pressure of a brake fluid in the internal flow path, wherein the pressure sensor mounting hole is open on the second surface. a master cylinder-integrated base body where a piston mounting hole where a piston of a master cylinder is provided so as to be capable of reciprocating, a reservoir tank for brake fluid storage connected to the piston mounting hole, and an internal flow path as a part of a brake fluid flow path allowing the piston mounting hole and the wheel cylinder to communicate with each other are formed; an inlet valve provided in an inlet valve mounting hole formed in the base body so as to be capable of reciprocating and opening and closing a part of the internal flow path through which a brake fluid flowing from the piston mounting hole to the wheel cylinder passes; and an outlet valve provided in an outlet valve mounting hole formed in the base body so as to be capable of reciprocating and opening and closing a part of the internal flow path through which a brake fluid flowing from the wheel cylinder to the accumulator passes, wherein the inlet valve mounting hole and the outlet valve mounting hole are open on a second surface in a case where a surface of the base body where an opening portion of the reservoir tank is formed is a first surface and a surface of the base body opposite to the first surface is the second surface, characterized in that the hydraulic pressure control device (1, 2) further comprises a pressure sensor provided in a pressure sensor mounting hole formed in the base body and detecting pressure of a brake fluid in the internal flow path, wherein the inlet valve mounting hole and the outlet valve mounting hole are open on a second surface in a case where a surface of the base body where an opening portion of the reservoir tank is formed is a first surface and a surface of the base body opposite to the first surface is the second surface, characterized in that the hydraulic pressure control device (1, 2) further comprises a pressure sensor provided in a pressure sensor mounting hole formed in the base body and detecting pressure of a brake fluid in the internal flow path, wherein the pressure sensor mounting hole is open on the second surface.