Calstock Signal Box containing just four levers was opened at 1 mile 55 chains mile post mileage from Bere Alston Station on March 2nd 1908. The block instruments were kept in the booking office on the Station. The section between Bere Alston Signal Box and here was operated under the Train Staff and Ticket system but only freight trains or non-passenger workings could pass here. The section forward to Gunnislake Signal Box was operated by the Electric Tablet system.
It was replaced in 1937 by a 10 lever-frame. There was no switching out apparatus.
In 1957 Calstock Signal Box, which was 1 mile 1,202 yards from Bere Alston Signal Box, was open on Mondays to Fridays from 5.35am until 10.30pm; on Saturdays from 5.35am until 10.40pm; and on Sundays between 8.30am and 12.50pm, 6.30pm until 7.45pm, and 9.15pm until 10.35pm. The Box was not provided with a closing switch.
Calstock Signal Box was closed on or as from May 5th 1968.