An electrode sheet for acquiring brain waves, which is a main sheet, and another electrode sheet, which is an auxiliary sheet, the main sheet, comprising: a sheet-shaped first flexible substrate; wiring comprising a plurality of first wirings formed on the first flexible substrate; a plurality of first electrodes formed on the first flexible substrate at positions that do not overlap with each other and electrically connected to the respective first wirings; and a first insulating layer laid on the first wiring, and also laid on the first flexible substrate, the first insulating layer comprising through holes so as to expose the first electrodes, the auxiliary sheet, comprising: a second flexible substrate formed into a sheet shape and a linear shape; a second wiring formed linearly along the second flexible substrate; a second electrode comprising a primary electrode formed on one end side of the flexible substrate and electrically connected to one end of the second wiring and a secondary electrode formed on the other end side of the flexible substrate and electrically connected to the other end of the second wiring; and a second insulating layer laid on the second wiring, and also laid on the second flexible substrate, the second insulating layer comprising through holes (131 A,131 B) so as to expose the primary and secondary electrodes (14A, 14B), wherein the first electrodes and the second electrodes are formed of a conductive material including conductive particles dispersed in a thermoplastic resin, and wherein the first electrode and the primary electrode of the second electrode are configured to be bonded to each other by thermal compression bonding with their exposed surfaces opposed to each other. the main sheet, comprising: a sheet-shaped first flexible substrate; wiring comprising a plurality of first wirings formed on the first flexible substrate; a plurality of first electrodes formed on the first flexible substrate at positions that do not overlap with each other and electrically connected to the respective first wirings; and a first insulating layer laid on the first wiring, and also laid on the first flexible substrate, the first insulating layer comprising through holes so as to expose the first electrodes, a sheet-shaped first flexible substrate; wiring comprising a plurality of first wirings formed on the first flexible substrate; a plurality of first electrodes formed on the first flexible substrate at positions that do not overlap with each other and electrically connected to the respective first wirings; and a first insulating layer laid on the first wiring, and also laid on the first flexible substrate, the first insulating layer comprising through holes so as to expose the first electrodes, the auxiliary sheet, comprising: a second flexible substrate formed into a sheet shape and a linear shape; a second wiring formed linearly along the second flexible substrate; a second electrode comprising a primary electrode formed on one end side of the flexible substrate and electrically connected to one end of the second wiring and a secondary electrode formed on the other end side of the flexible substrate and electrically connected to the other end of the second wiring; and a second insulating layer laid on the second wiring, and also laid on the second flexible substrate, the second insulating layer comprising through holes (131 A,131 B) so as to expose the primary and secondary electrodes (14A, 14B), wherein the first electrodes and the second electrodes are formed of a conductive material including conductive particles dispersed in a thermoplastic resin, and wherein a second flexible substrate formed into a sheet shape and a linear shape; a second wiring formed linearly along the second flexible substrate; a second electrode comprising a primary electrode formed on one end side of the flexible substrate and electrically connected to one end of the second wiring and a secondary electrode formed on the other end side of the flexible substrate and electrically connected to the other end of the second wiring; and a second insulating layer laid on the second wiring, and also laid on the second flexible substrate, the second insulating layer comprising through holes (131 A,131 B) so as to expose the primary and secondary electrodes (14A, 14B), wherein the first electrodes and the second electrodes are formed of a conductive material including conductive particles dispersed in a thermoplastic resin, and wherein the first electrode and the primary electrode of the second electrode are configured to be bonded to each other by thermal compression bonding with their exposed surfaces opposed to each other.