Panasonic light curtain SF2-A / SF2-N series, area sensor NA40 series, and SF1-N series can be replaced with the SF2B series using the current mounting holes and connection cables. The light curtain unit has a built-in monitoring function for external devices (such as fused relay monitoring). This supports the construction of light curtain peripheral safety circuits which do not use a safety relay unit, and contributes to reduced costs and a more compact control panel. In addition, a connectable control unit is used, so that a safety circuit that is easy to construct and easy to install can be selected. By using a single corner mirror, light curtain and peripheral safety circuit for one set are eliminated. Enables significant cost reduction and savings on wiring. The control category is unchanged. When setting up the light curtains in the L-shape or U-shape, usually two or three sets of the light curtains are required. However, using the corner mirror to reflect the laser light allows only one set of the light curtains to be set up at the L-shape or U-shape. The inner unit is protected by a cylindrical inner case. The seams of unit and lens surfaces have been greatly reduced, so that particles of oil mists and dust are prevented from getting in.