A specimen transfer device, comprising: a plurality of trays, each being configured to convey a plurality of carriers having unique identification information, each carrier being configured to hold one or more specimen containers; and a transfer unit configured to transfer a specimen container to a carrier on one of the plurality of trays, wherein the specimen transfer device includes: a unit configured to group at least two trays out of the plurality of trays, a control unit configured to execute control such that the transfer unit transfers a specimen container to a first carrier retained on a tray, and transference of a next specimen container is switched to a second carrier retained in a different tray allocated to a same group when the first carrier is fully loaded; a reading device configured to read the unique identification information for the second carrier; and a conveyance line; characterized in that the conveyance line is capable of bidirectionally conveying a carrier discharged from the plurality of trays, wherein the reading device is disposed at one end of the conveyance line, wherein the conveyance line is configured to: convey, in a first direction, a carrier before transferring a specimen container and place the carrier in a position where the reading device can execute reading; return, to the respective tray, the carrier having its unique identification information read; and convey, in a second direction, a carrier finished with transference of specimen containers; and wherein the specimen transfer device is configured such that conveying the second carrier in the first direction to the position where the reading device can execute reading, reading the unique identification information for the second carrier, and returning the second carrier having its unique identification information read to the respective tray, happen simultaneously with the transfer of specimen containers to the first carrier. a plurality of trays, each being configured to convey a plurality of carriers having unique identification information, each carrier being configured to hold one or more specimen containers; and a transfer unit configured to transfer a specimen container to a carrier on one of the plurality of trays, wherein the specimen transfer device includes: a unit configured to group at least two trays out of the plurality of trays, a control unit configured to execute control such that the transfer unit transfers a specimen container to a first carrier retained on a tray, and transference of a next specimen container is switched to a second carrier retained in a different tray allocated to a same group when the first carrier is fully loaded; a reading device configured to read the unique identification information for the second carrier; and a conveyance line; characterized in that the conveyance line is capable of bidirectionally conveying a carrier discharged from the plurality of trays, wherein the reading device is disposed at one end of the conveyance line, wherein the conveyance line is configured to: convey, in a first direction, a carrier before transferring a specimen container and place the carrier in a position where the reading device can execute reading; return, to the respective tray, the carrier having its unique identification information read; and convey, in a second direction, a carrier finished with transference of specimen containers; and wherein the specimen transfer device is configured such that conveying the second carrier in the first direction to the position where the reading device can execute reading, reading the unique identification information for the second carrier, and returning the second carrier having its unique identification information read to the respective tray, happen simultaneously with the transfer of specimen containers to the first carrier. a unit configured to group at least two trays out of the plurality of trays, a control unit configured to execute control such that the transfer unit transfers a specimen container to a first carrier retained on a tray, and transference of a next specimen container is switched to a second carrier retained in a different tray allocated to a same group when the first carrier is fully loaded; a reading device configured to read the unique identification information for the second carrier; and a conveyance line; characterized in that the conveyance line is capable of bidirectionally conveying a carrier discharged from the plurality of trays, wherein the reading device is disposed at one end of the conveyance line, wherein the conveyance line is configured to: convey, in a first direction, a carrier before transferring a specimen container and place the carrier in a position where the reading device can execute reading; return, to the respective tray, the carrier having its unique identification information read; and convey, in a second direction, a carrier finished with transference of specimen containers; and wherein the specimen transfer device is configured such that conveying the second carrier in the first direction to the position where the reading device can execute reading, reading the unique identification information for the second carrier, and returning the second carrier having its unique identification information read to the respective tray, happen simultaneously with the transfer of specimen containers to the first carrier.