A pressure exchanger includes a rotator disposed with pressure transmission sections around a rotation axis. Each pressure transmission section is formed such that a first flow path and a second flow path are communicated with each other. A first lateral member is formed with: first fluid inflow paths guiding the first fluid to the first flow paths; second fluid outflow paths guiding, from the second flow paths, second fluid obtained after pressure exchange with the first fluid; second fluid inflow paths guiding the second fluid to the second flow paths; and first fluid outflow paths guiding, from the first flow paths, first fluid obtained after pressure exchange with the second fluid in the thickness direction. A second lateral member is rotatably sandwiching the rotator between the second lateral member and the first lateral member.