A pressure detector that includes a case connectable to a flow route for liquid, and a membrane member attached inside the case and with which a liquid-phase portion to be supplied with the liquid in the flow route and a gas-phase portion to be supplied with gas are separated from each other, the membrane member being displaceable in accordance with a pressure of the liquid supplied to the liquid-phase portion, the pressure detector detecting the pressure of the liquid in the flow route by detecting a pressure in the gas-phase portion, the pressure detector comprising: an inlet port including a connecting portion (C1b) connectable to the flow route for the liquid, and a flow-route portion (C1a) through which the liquid flows into an inlet opening of the liquid-phase portion; and an outlet port including a connecting portion (C2b) connectable to the flow route for the liquid, and a flow-route portion (C2a) through which the liquid having flowed into the liquid-phase portion is discharged from an outlet opening, wherein at least one of the flow-route portion (C1a) of the inlet port and the flow-route portion (C2a) of the outlet port is configured such that an incoming direction (α) or an outgoing direction (β) of the liquid is inclined with respect to an attaching plane defined for the membrane member, characterized in that at least one of the inlet port and the outlet port is configured such that a virtual line (Lb) connecting a first center point (Pa) as a center position of the flow-route portion (C1a, C2a) in a boundary plane defined between the flow-route portion (C1a, C2a) and the connecting portion (C1b, C2b) and a second center point (Pb) as a center position of the flow-route portion (C1a, C2a) in a plane extending parallel to the boundary plane and containing an opening edge of the inlet opening or the outlet opening is inclined with respect to a center line of the connecting portion (C1b, C2b). a case connectable to a flow route for liquid, and a membrane member attached inside the case and with which a liquid-phase portion to be supplied with the liquid in the flow route and a gas-phase portion to be supplied with gas are separated from each other, the membrane member being displaceable in accordance with a pressure of the liquid supplied to the liquid-phase portion, the pressure detector detecting the pressure of the liquid in the flow route by detecting a pressure in the gas-phase portion, the pressure detector comprising: an inlet port including a connecting portion (C1b) connectable to the flow route for the liquid, and a flow-route portion (C1a) through which the liquid flows into an inlet opening of the liquid-phase portion; and an outlet port including a connecting portion (C2b) connectable to the flow route for the liquid, and a flow-route portion (C2a) through which the liquid having flowed into the liquid-phase portion is discharged from an outlet opening, wherein at least one of the flow-route portion (C1a) of the inlet port and the flow-route portion (C2a) of the outlet port is configured such that an incoming direction (α) or an outgoing direction (β) of the liquid is inclined with respect to an attaching plane defined for the membrane member, characterized in that at least one of the inlet port and the outlet port is configured such that a virtual line (Lb) connecting a first center point (Pa) as a center position of the flow-route portion (C1a, C2a) in a boundary plane defined between the flow-route portion (C1a, C2a) and the connecting portion (C1b, C2b) and a second center point (Pb) as a center position of the flow-route portion (C1a, C2a) in a plane extending parallel to the boundary plane and containing an opening edge of the inlet opening or the outlet opening is inclined with respect to a center line of the connecting portion (C1b, C2b). an inlet port including a connecting portion (C1b) connectable to the flow route for the liquid, and a flow-route portion (C1a) through which the liquid flows into an inlet opening of the liquid-phase portion; and an outlet port including a connecting portion (C2b) connectable to the flow route for the liquid, and a flow-route portion (C2a) through which the liquid having flowed into the liquid-phase portion is discharged from an outlet opening, wherein at least one of the flow-route portion (C1a) of the inlet port and the flow-route portion (C2a) of the outlet port is configured such that an incoming direction (α) or an outgoing direction (β) of the liquid is inclined with respect to an attaching plane defined for the membrane member, characterized in that at least one of the inlet port and the outlet port is configured such that a virtual line (Lb) connecting a first center point (Pa) as a center position of the flow-route portion (C1a, C2a) in a boundary plane defined between the flow-route portion (C1a, C2a) and the connecting portion (C1b, C2b) and a second center point (Pb) as a center position of the flow-route portion (C1a, C2a) in a plane extending parallel to the boundary plane and containing an opening edge of the inlet opening or the outlet opening is inclined with respect to a center line of the connecting portion (C1b, C2b).