A concentration device suitable for dielectrophoresis, comprising: a first substrate; a second substrate provided so as to face the first substrate; a flow path formed between the first substrate and the second substrate; a first pillar electrode line disposed in the flow path; and a second pillar electrode line disposed in the flow path, wherein the first pillar electrode line and the second pillar electrode line are parallel to an X-axis direction; the first pillar electrode line and the second pillar electrode line include first pillar electrodes and second pillar electrodes; each of the first pillar electrodes includes a first vertex P1 and a second vertex P2; each of the second pillar electrodes includes a first vertex Q1 and a second vertex Q2; a line segment between the first vertex P1 and the second vertex P2 which are included in each of the first pillar electrodes 301 is parallel to the X-axis direction; a line segment between the first vertex Q1 and the second vertex Q2 which are included in each of the second pillar electrodes 302 is parallel to a Y-axis direction; the X-axis direction is perpendicular to the Y-axis direction in a top view; a pillar electrode group is composed of a left-side first pillar electrode selected from the first pillar electrodes included in the second pillar electrode line; a right-side first pillar electrode selected from the first pillar electrodes included in the second pillar electrode line; a second pillar electrode selected from the second pillar electrodes included in the first pillar electrode line; and a second pillar electrode selected from the second pillar electrodes included in the second pillar electrode line; the left-side first pillar electrode and the right--side first pillar electrode are adjacent to each other in a top view in such a manner that the second vertex P2 of the left-side first pillar electrode and the first vertex P1 of the right-side first pillar electrode face each other; a line which passes through the second vertex Q2 of the second pillar electrode and the first vertex Q1 of the second pillar electrode is parallel to the Y-axis direction; and the following mathematical formula is satisfied: L 3 ≥ 5 micrometers where L 3 = A 1 − A 2, A1 represents a distance between the second vertex Q2 of the second pillar electrode and a center point O; A2 represents a distance between the first vertex Q1 of the second pillar electrode and the center point O; the center point O is an intersection point of a line segment P and a line segment Q, the line segment Q is a line segment between the second vertex Q2 of the second pillar electrode and the first vertex Q1 of the second pillar electrode; and the line segment P is a line segment between the second vertex P2 of the left-side first pillar electrode and the first vertex P1 of the right-side first pillar electrode. a first substrate; a second substrate provided so as to face the first substrate; a flow path formed between the first substrate and the second substrate; a first pillar electrode line disposed in the flow path; and a second pillar electrode line disposed in the flow path, wherein the first pillar electrode line and the second pillar electrode line are parallel to an X-axis direction; the first pillar electrode line and the second pillar electrode line include first pillar electrodes and second pillar electrodes; each of the first pillar electrodes includes a first vertex P1 and a second vertex P2; each of the second pillar electrodes includes a first vertex Q1 and a second vertex Q2; a line segment between the first vertex P1 and the second vertex P2 which are included in each of the first pillar electrodes 301 is parallel to the X-axis direction; a line segment between the first vertex Q1 and the second vertex Q2 which are included in each of the second pillar electrodes 302 is parallel to a Y-axis direction; the X-axis direction is perpendicular to the Y-axis direction in a top view; a pillar electrode group is composed of a left-side first pillar electrode selected from the first pillar electrodes included in the second pillar electrode line; a right-side first pillar electrode selected from the first pillar electrodes included in the second pillar electrode line; a second pillar electrode selected from the second pillar electrodes included in the first pillar electrode line; and a second pillar electrode selected from the second pillar electrodes included in the second pillar electrode line; the left-side first pillar electrode and the right--side first pillar electrode are adjacent to each other in a top view in such a manner that the second vertex P2 of the left-side first pillar electrode and the first vertex P1 of the right-side first pillar electrode face each other; a line which passes through the second vertex Q2 of the second pillar electrode and the first vertex Q1 of the second pillar electrode is parallel to the Y-axis direction; and the following mathematical formula is satisfied: L 3 ≥ 5 micrometers where L 3 = A 1 − A 2, A1 represents a distance between the second vertex Q2 of the second pillar electrode and a center point O; A2 represents a distance between the first vertex Q1 of the second pillar electrode and the center point O; the center point O is an intersection point of a line segment P and a line segment Q, the line segment Q is a line segment between the second vertex Q2 of the second pillar electrode and the first vertex Q1 of the second pillar electrode; and the line segment P is a line segment between the second vertex P2 of the left-side first pillar electrode and the first vertex P1 of the right-side first pillar electrode.