3D printer, which is configured to build up a three-dimensional component, for example a casting mold or a foundry core, in layers by forming layers of particulate construction material, for example containing sand particles, lying one upon the other and by selectively solidifying a partial region of the respective construction material layer, and which is configured to build up one or more first three-dimensional components in a first construction space which is arranged in the 3D printer, and simultaneously one or more second three-dimensional components in a second construction space which is arranged adjacent to the first construction space at a horizontal distance therefrom in the 3D printer, having a coating device arrangement which is displaceable across the first and the second construction space (B1, B2) in a first horizontal direction (H 1), to supply the first and the second construction space (B1, B2) with construction material in the form of a respectively uniform construction material layer of the construction material to be solidified, and with a common printing device which is displaceable across the first and the second construction space (B1, B2) in a second horizontal direction (H 2), which is perpendicular to the first horizontal direction (H 1), to selectively solidify a partial region of a previously applied construction material layer of the respective construction space by a controlled output of a flowable treatment agent, wherein the common printing device comprises a common printing head having one or more printing nozzles, which is configured to serve both the first construction space and the second construction space, wherein the first construction space and the second construction space have two long sides and two short sides in top view, and wherein the first horizontal direction (H 1) is perpendicular to the long sides and/or parallel to the short sides. which is configured to build up a three-dimensional component, for example a casting mold or a foundry core, in layers by forming layers of particulate construction material, for example containing sand particles, lying one upon the other and by selectively solidifying a partial region of the respective construction material layer, and which is configured to build up one or more first three-dimensional components in a first construction space which is arranged in the 3D printer, and simultaneously one or more second three-dimensional components in a second construction space which is arranged adjacent to the first construction space at a horizontal distance therefrom in the 3D printer, having a coating device arrangement which is displaceable across the first and the second construction space (B1, B2) in a first horizontal direction (H 1), to supply the first and the second construction space (B1, B2) with construction material in the form of a respectively uniform construction material layer of the construction material to be solidified, and with a common printing device which is displaceable across the first and the second construction space (B1, B2) in a second horizontal direction (H 2), which is perpendicular to the first horizontal direction (H 1), to selectively solidify a partial region of a previously applied construction material layer of the respective construction space by a controlled output of a flowable treatment agent, wherein the common printing device comprises a common printing head having one or more printing nozzles, which is configured to serve both the first construction space and the second construction space, wherein the first construction space and the second construction space have two long sides and two short sides in top view, and wherein the first horizontal direction (H 1) is perpendicular to the long sides and/or parallel to the short sides.