An electromagnetic contact apparatus, wherein: two electromagnetic contact devices (1a, 1b) are arranged adjacently, and the two electromagnetic contact devices are linked by detachably mounting, on case-side mounting portions of these electromagnetic contact devices, unit-side mounting portions (2c-2f) of a reversible unit that serves as an ancillary unit and prohibits simultaneous input of the two electromagnetic contact devices, and wherein for each electromagnetic contact device (1a, 1b): a body case is provided with the case-side mounting portions on which one or more ancillary units (2, 3a, 3b, 4a, 4b), which can be of different types, can be mounted simultaneously, the unit-side mounting portions (2c-2f, 3a4-3a5, 20a-20c) of the one or more ancillary units, which can be of different types, are detachably mounted on the case-side mounting portions, and the electromagnetic contact device has, arranged within the body case, a movable contact support (7a, 7b), an electromagnet that moves the movable contact support by exciting a coil, and an operation indicator piece (7a1) that is formed integrally with the movable contact support and exposed to the outside through an indicator window (6c2) provided on a side of the body case on which the ancillary units are mounted, and wherein the unit-side mounting portion (20a-20c) for one or two auxiliary contact point units (4a, 4b) serving as the ancillary unit and provided with auxiliary circuit terminals is detachably mounted on an inter-unit mounting portion (2c-2f) provided in the reversible unit, characterized in that the unit-side mounting portion (3a4, 3a5) for one or two surge absorption units (3a, 3b) serving as the ancillary unit and absorbing surge voltages generated by the electromagnet is detachably mounted on a case-side mounting portion (15, 16) of the electromagnetic contact device (1a, 1b), and the surge absorption unit (3a, 3b) is detachably mounted on the electromagnetic contact device (1a, 1b) spanning the reversible unit. two electromagnetic contact devices (1a, 1b) are arranged adjacently, and the two electromagnetic contact devices are linked by detachably mounting, on case-side mounting portions of these electromagnetic contact devices, unit-side mounting portions (2c-2f) of a reversible unit that serves as an ancillary unit and prohibits simultaneous input of the two electromagnetic contact devices, and wherein for each electromagnetic contact device (1a, 1b): a body case is provided with the case-side mounting portions on which one or more ancillary units (2, 3a, 3b, 4a, 4b), which can be of different types, can be mounted simultaneously, the unit-side mounting portions (2c-2f, 3a4-3a5, 20a-20c) of the one or more ancillary units, which can be of different types, are detachably mounted on the case-side mounting portions, and the electromagnetic contact device has, arranged within the body case, a movable contact support (7a, 7b), an electromagnet that moves the movable contact support by exciting a coil, and an operation indicator piece (7a1) that is formed integrally with the movable contact support and exposed to the outside through an indicator window (6c2) provided on a side of the body case on which the ancillary units are mounted, and wherein the unit-side mounting portion (20a-20c) for one or two auxiliary contact point units (4a, 4b) serving as the ancillary unit and provided with auxiliary circuit terminals is detachably mounted on an inter-unit mounting portion (2c-2f) provided in the reversible unit, characterized in that the unit-side mounting portion (3a4, 3a5) for one or two surge absorption units (3a, 3b) serving as the ancillary unit and absorbing surge voltages generated by the electromagnet is detachably mounted on a case-side mounting portion (15, 16) of the electromagnetic contact device (1a, 1b), and the surge absorption unit (3a, 3b) is detachably mounted on the electromagnetic contact device (1a, 1b) spanning the reversible unit. a body case is provided with the case-side mounting portions on which one or more ancillary units (2, 3a, 3b, 4a, 4b), which can be of different types, can be mounted simultaneously, the unit-side mounting portions (2c-2f, 3a4-3a5, 20a-20c) of the one or more ancillary units, which can be of different types, are detachably mounted on the case-side mounting portions, and the electromagnetic contact device has, arranged within the body case, a movable contact support (7a, 7b), an electromagnet that moves the movable contact support by exciting a coil, and an operation indicator piece (7a1) that is formed integrally with the movable contact support and exposed to the outside through an indicator window (6c2) provided on a side of the body case on which the ancillary units are mounted, and wherein the unit-side mounting portion (20a-20c) for one or two auxiliary contact point units (4a, 4b) serving as the ancillary unit and provided with auxiliary circuit terminals is detachably mounted on an inter-unit mounting portion (2c-2f) provided in the reversible unit, characterized in that the unit-side mounting portion (3a4, 3a5) for one or two surge absorption units (3a, 3b) serving as the ancillary unit and absorbing surge voltages generated by the electromagnet is detachably mounted on a case-side mounting portion (15, 16) of the electromagnetic contact device (1a, 1b), and the surge absorption unit (3a, 3b) is detachably mounted on the electromagnetic contact device (1a, 1b) spanning the reversible unit.