PURPOSE: To eliminate dead spaces around a locking mechanism which is provided for a socket mounting an electronic circuit substrate for locking the circuit substrate.

CONSTITUTION: In the socket for an electronic circuit substrate, which is in a U shape, has an electronic circuit substrate inserted at its center section, and is provided with a locking mechanism at its both side sections, which locks both side sections of the circuit substrate, the socket 10 is provided with a housing section 10c at its side section 10b along its longer direction. And the locking mechanism 12 is equipped with a rotary type latch 13 which is housed in the housing section in such a way that it can be rotated along the longer direction, locks the side section of the circuit substrate at a first rotating position, and releases its lock at a second rotating position in the opposite direction to that of the first rotating position, and with a spring member 14 which energizes the rotary type latch housed in the housing section to the first rotating position.