A flow rate adjustment device that adjusts a flow rate of a fluid circulating through an internal flow path, the flow rate adjustment device comprising: a diaphragm integrated valve body section which includes a base which is formed in a shaft-like shape along the axis line, a diaphragm section which is coupled to an outer peripheral surface of the base and is formed in an annular shape about the axis line and in a thin film shape, and an annular section which includes an inner peripheral surface coupled to an outer peripheral end of the diaphragm section and is formed in a annular shape, and is configured to move along an axis line within a valve chest and including a valve surface; a valve seat section including a valve seat surface, an internal flow path being provided in the valve seat section; and a transfer mechanism coupled to the diaphragm integrated valve body section and configured to cause the diaphragm integrated valve body section to move along the axis line to adjust a distance between the valve surface and the valve seat surface, wherein the valve seat surface is disposed at a position facing the valve surface and is provided around a flow path opening which allows the valve chest and the internal flow path to communicate with each other, the transfer mechanism adjusts the flow rate of the fluid circulating between the valve chest and the internal flow path by adjusting the distance between the valve surface and the valve seat surface, characterized in that: the valve surface and the valve seat surface form an acute angle (θ) with the axis line and are disposed in parallel, the valve surface and the valve seat surface are surfaces formed in a planar shape, and a length of a line of intersection between a plane orthogonal to the axis line and the valve seat surface is longer than a length (L1, L2) of a line of intersection between the plane and the valve surface. a diaphragm integrated valve body section which includes a base which is formed in a shaft-like shape along the axis line, a diaphragm section which is coupled to an outer peripheral surface of the base and is formed in an annular shape about the axis line and in a thin film shape, and an annular section which includes an inner peripheral surface coupled to an outer peripheral end of the diaphragm section and is formed in a annular shape, and is configured to move along an axis line within a valve chest and including a valve surface; a valve seat section including a valve seat surface, an internal flow path being provided in the valve seat section; and a transfer mechanism coupled to the diaphragm integrated valve body section and configured to cause the diaphragm integrated valve body section to move along the axis line to adjust a distance between the valve surface and the valve seat surface, wherein the valve seat surface is disposed at a position facing the valve surface and is provided around a flow path opening which allows the valve chest and the internal flow path to communicate with each other, the transfer mechanism adjusts the flow rate of the fluid circulating between the valve chest and the internal flow path by adjusting the distance between the valve surface and the valve seat surface, characterized in that: the valve surface and the valve seat surface form an acute angle (θ) with the axis line and are disposed in parallel, the valve surface and the valve seat surface are surfaces formed in a planar shape, and a length of a line of intersection between a plane orthogonal to the axis line and the valve seat surface is longer than a length (L1, L2) of a line of intersection between the plane and the valve surface. the valve surface and the valve seat surface form an acute angle (θ) with the axis line and are disposed in parallel, the valve surface and the valve seat surface are surfaces formed in a planar shape, and a length of a line of intersection between a plane orthogonal to the axis line and the valve seat surface is longer than a length (L1, L2) of a line of intersection between the plane and the valve surface.