| CPC H05K 7/1474 (2013.01) [H05K 7/1465 (2013.01)] | 13 Claims |

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1. A programmable logic controller comprising:
a base unit; and
a plurality of module units to be connected to the base unit,
wherein
the base unit comprises:
a substrate having a plurality of base-side connectors and electrically connecting the plurality of module units via the plurality of base-side connectors;
a base case having an opening through which one of the plurality of base-side connectors is exposed and housing the substrate; and
at least one holding part to hold a connection unit which is one of the plurality of module units,
wherein
the connection unit comprises:
a module-side connector to be connected to one of the plurality of base-side connectors;
an engagement mechanism to be detachably engaged with the at least one holding part of the base unit; and
a module case having a fitting tenon formed in such a manner as to be fitted with the base case and to surround the module-side connector,
wherein
the programmable logic controller further comprises:
an elastic member to exert a force in a first direction, which is a direction in which the connection unit moves away from the base unit, for pressing the engagement mechanism of the connection unit against the at least one holding part of the base unit; and
a sealing member to seal a gap between the base case and the fitting tenon of the module case,
and wherein
the at least one holding part is provided in plurality to form pairs, and
the pair of holding parts has at least one slant face inclined with respect to the first direction such that the force exerted by the elastic member is applied in a second direction intersecting the first direction.
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