A laser marker comprising: a laser oscillation unit having an expander and configured to emit laser light; and a base having a scanning unit, the laser oscillation unit being removably mounted to the scanning unit by sliding with being placed on the base, the scanning unit being configured to scan the laser light emitted from the laser oscillation unit, and an insertion part provided to the scanning unit, the expander of the laser oscillation unit being inserted into the insertion part in a case the laser oscillation unit is mounted, wherein the base comprises: a first guide portion (56, 58); and a restriction part configured to restrict sliding of the laser oscillation unit on the base by butting against the laser oscillation unit, and wherein the laser oscillation unit comprises: a second guide portion (90, 92) configured to define a mounting direction of the laser oscillation unit by engaging with the first guide portion (56, 58) of the base; and a contact part configured to be in contact with the restriction part of the base in a case the laser oscillation unit is mounted to the scanning unit, characterized in that the first guide portion (56, 58) comprises: an upstream-side first guide portion arranged on an upstream side of the base with respect to the mounting direction; and a downstream-side first guide portion arranged on a further downstream side than the upstream-side first guide portion with respect to the mounting direction, and wherein the second guide portion (90, 92), in the laser oscillation unit configured to slide in the mounting direction on the base with respect to the mounting direction, comprises: an upstream-side second guide portion located on an upstream side of the mounting direction; and a downstream-side second guide portion located on a further downstream side than the upstream-side second guide portion with respect to the mounting direction. a laser oscillation unit having an expander and configured to emit laser light; and a base having a scanning unit, the laser oscillation unit being removably mounted to the scanning unit by sliding with being placed on the base, the scanning unit being configured to scan the laser light emitted from the laser oscillation unit, and an insertion part provided to the scanning unit, the expander of the laser oscillation unit being inserted into the insertion part in a case the laser oscillation unit is mounted, wherein the base comprises: a first guide portion (56, 58); and a restriction part configured to restrict sliding of the laser oscillation unit on the base by butting against the laser oscillation unit, and a first guide portion (56, 58); and a restriction part configured to restrict sliding of the laser oscillation unit on the base by butting against the laser oscillation unit, and wherein the laser oscillation unit comprises: a second guide portion (90, 92) configured to define a mounting direction of the laser oscillation unit by engaging with the first guide portion (56, 58) of the base; and a contact part configured to be in contact with the restriction part of the base in a case the laser oscillation unit is mounted to the scanning unit, a second guide portion (90, 92) configured to define a mounting direction of the laser oscillation unit by engaging with the first guide portion (56, 58) of the base; and a contact part configured to be in contact with the restriction part of the base in a case the laser oscillation unit is mounted to the scanning unit, characterized in that the first guide portion (56, 58) comprises: an upstream-side first guide portion arranged on an upstream side of the base with respect to the mounting direction; and a downstream-side first guide portion arranged on a further downstream side than the upstream-side first guide portion with respect to the mounting direction, and an upstream-side first guide portion arranged on an upstream side of the base with respect to the mounting direction; and a downstream-side first guide portion arranged on a further downstream side than the upstream-side first guide portion with respect to the mounting direction, and wherein the second guide portion (90, 92), in the laser oscillation unit configured to slide in the mounting direction on the base with respect to the mounting direction, comprises: an upstream-side second guide portion located on an upstream side of the mounting direction; and a downstream-side second guide portion located on a further downstream side than the upstream-side second guide portion with respect to the mounting direction. an upstream-side second guide portion located on an upstream side of the mounting direction; and a downstream-side second guide portion located on a further downstream side than the upstream-side second guide portion with respect to the mounting direction.