-- 参考サイト -- Checking The Boxes, Getting The Input: http://www.laceysnr.com/2013/04/checking-boxes-geting-input.html

CheckingTheBoxesController .cls

public with sharing class CheckingTheBoxesController {

    public Map<Id, Boolean> selected {get; set;}
    public List<Opportunity> opportunities {get; set;}
    public Boolean forAll {get; set;}
    
    public CheckingTheBoxesController() {
        this.selected = new Map<Id, Boolean>();
        this.opportunities = new List<Opportunity>();
        
        for(Opportunity o : [select Id, Name from Opportunity])
        {
            this.selected.Put(o.Id, false);
            this.opportunities.Add(o);
        }
    }
    
    public void ToggleAll()
    {
        for(Id oppty : this.selected.keyset())
        {
            this.selected.Put(oppty, this.forAll);
        }
    }
}

CheckingTheBoxesPage.page

<apex:page controller="CheckingTheBoxesController" tabStyle="Opportunity" id="page">
    <apex:form>
        <apex:pageBlock>
            <apex:pageBlockTable value="{!opportunities}" var="o" id="list">
                <apex:column style="width:30px">
                    <apex:facet name="header">
                        <apex:inputCheckbox value="{!forAll}">
                            <apex:actionSupport event="onchange" action="{!ToggleAll}" rerender="list"/>
                        </apex:inputCheckbox>
                    </apex:facet>
                    <apex:inputCheckbox value="{!selected[o.Id]}"/>
                </apex:column>
                <apex:column>
                    <apex:outputField value="{!o.Name}"/>
                </apex:column>
            </apex:pageBlockTable>
        </apex:pageBlock>
    </apex:form>
</apex:page>