Collimator module, X-ray detector, X-ray CT device, and assembling method of collimator module

A collimator module (10A) comprises a plurality of collimator single plates (11) having a pair of long sides and a pair of short sides and a pair of blocks (12) including a plurality of first grooves (125) extending along an irradiation direction of the X-rays. The short sides are inserted into the first grooves to support the collimator single plates. A supporting member is configured to cover the long sides from an incident side and an emission side of the X-rays. The supporting member includes an incident side fixing sheet (13) and an emission side fixing sheet (15) each having a plurality of second grooves into which the long sides are inserted to support the plurality of collimator single plates. The fixing sheets cover the first grooves and at least a portion of each of the long sides.